Can I decline being promoted to Corporal?

If I was your BN CSM who approved you passing the board I'd undo it upon reading this. You want to be a NCO and be a Team Leader, have been approved to become one, but don't want to do the job until you get the $$$? That's not being a leader, that's not what an NCO does.
Being a Corporal is essentially being a SGT just without the extra $. Your unit wants you to do your new position while you wait to finish BLC - not to get cheap NCO labor out of you.

Check it out, (this isn't meant to be rude, but take it for what it's worth). There will be times in your career when your placed in a position of higher responsibility without the pay. From example, as a SGT I served 13 months rated time as a PSG. I spent a few months on deployment serving in a 1LT position, neither time did I get a pay bump, it just is what it is. Understand that now and it won't hit you as hard when you're one rank and they have you take on higher responsibilities. Take the corporal, it does nothing but help you prepare to actual promote to Sergeant.

And yes I'm pretty sure you can refuse it, but it will bite you in the ass.

While I said you can talk to your leadership, I want you to take something into account. When I was a SGT, I was doing the duties of a SSG, until I found myself as a SGT doing the duties of a SFC. I was put in those higher leadership roles because the powers that be saw the potential. I sure as hell wasn't getting the SSG not SFC pay back then. But, I still did my job and I still led my Soldiers.

I'm normally pretty chill with questions on this forum but attitudes like this really burn my butt. You don't want to take responsibility?!?! Then what the hell are you doing going to BLC or taking up a slot at ranger school?
A question like yours demonstrates unequivocally that you are not fit to lead -- at least not with your present attitude. Your first thought is about pay, not results. You focus is "me, me, me," not "mission first and always." I feel sorry for your soldiers because it doesn't look like you have much of the NCO creed in your heart.
Let me put you straight, Specialist. An NCO puts his soldiers first - ALWAYS. They're the first ones to get chow. They're the first ones to get a couple hours of sleep. They're the first ones in line for anything good.
It's your job as a leader to stand in the breach for them. It's your job to take the hit from the 1SG when one of your guys screws up because, guess what? You are responsible for your troops. If any of this sounds like something you don't want to do then you are NOT NCO material.
Being an NCO is not about pay. It's about being a key player in the team. But if you got $ in your eyes you are not looking out for your team -- you're too busy looking out for yourself. Sorry, but you are not the kind of guy I would want in my foxhole.
One thing, though: if this is how you feel you won't get many more stripes. You can bet your butt the soldiers you lead will figure you out quick. Their performance will be in the same place as your attitude: the toilet. A few crappy NCOER's (or whatever they call them nowadays) and you'll be a career E-6 at twenty facing your RCP.
If your thinking is what it looks like, you should get out and let someone who wants to be a leader do the work you're too special to do.

That's your choice, and you have every right to it. All you have to do is not sign the 4187.

But if you don't want additional responsibility until you get the additional money, I have some bad news for you...
Not only did you join the wrong organization for that, but most of the organizations in the private sector will also be wrong for you.

It's been mentioned in most of these posts, but E4s work as TM LDRs. SGTs work as SLs.
SSGs and SGTs work as PSGs. I have seen SFCs hold a CPT billet overseas.
In the private sector I have seen junior salaried and hourly employees manage programs and people prior to getting paid management.

That's just the way the world works; all too often the job needs to be filled faster than the paperwork or requirements can be completed.

But if that's not you, then you will be punching a time clock for as long as you are working your post-military career.

LMAO - you can be slotted as a team leader and have the responsibility even as a SPC - the lateral promotion gives your orders more weight. You do not get to decide if you want the position or not, Command makes the decision, and if that is where they want you, then that is what you will do. Do you want to lead or is it just a paycheck.

Brother, I would think long and hard about not wanting that hard stripe. The Army is a small world, and the Deuce makes it even smaller. If I ever had any Junior Leader that I was grooming into the NCO Corps tell me that they didn’t want the responsibility until they were getting the pay I’d immediately begin vesting my efforts in another candidate that was up to the burden of leadership and I’d let my peers know they weren’t quite ready for the next step. That’s not personal, it’s stewardship of the profession. An Effective Leader is constantly going to be tasked with duties and responsibilities beyond what rank they wear.

So are you saying, it's all about the money? Are you better than anybody else who was a CPL or was a SPC, made into an acting team leader w/o the stripes? You are wearing a Falcon crest, just How many CPL's have you seen in the Regiment. My 14 yrs. I saw 3- 1- SVN vet who got busted every 4-5 months of drunk. Disorderly or 2 days AWOL. I was the 2nd while waiting for E5 points to come down, and the Asst Supply NCOIC who doubled as the company armorer. If this gets around, I would worry about changing stripes, you could just wait for hard stripes sometime down the road and any further progression might be slow.

WTF, SGT (Join to see), if you’re that concerned about money vs position, just ETS. Somewhere there’s a private sector company that will be happy to exploit your labor for less than the prevailing wage. At least you’ll be free to quit any time you want.

You can still be a team leader as a SPC, you don't have to be a CPL to be in a leadership position.

If your goal is to pass Ranger School then you need to be in a leadership position practicing leadership. Contrary to popular belief Ranger School is not just some "gut check" to see if you're tough enough. You are being evaluated in a leadership position and being graded upon your performance as a leader. Ranger School literally IS being a Team Leader, and a Squad Leader, and a PL and PSG over and over again. The people who do the best are the ones with leadership experience. If you think you're going to walk in there with zero leadership experience under the best of conditions - a garrison environment - and expect to perform well leading Rangers under the worst possible conditions, you will become a resident of the RTB Gulag