Can I pin myself if I’m on PCs leave? Or should I wait to arrive at my new unit?

I personally would wait. Trust me getting pinned from SPC to SGT is a big deal. Don't pin your self. Communicate, communicate, communicate with your new sponsor in your new unit. Inform them that you got promoted. Every unit is the same with a traditional E-4 to E-5 promotion but different. Some just do an in ceremony. Others will do a company wide ceremony. Plus all units that I have been in doesn't matter what rank you were going too it was mandatory to have at least 1 family member there pinning you (that was when we actually wore pins not velcro). Trust if you start off on the correct foot, people will remember that and go to bat for you. If start on the wrong foot. It will take you FOREVER to gain the respect of others. Remember you want the respect from person to person not respect of person to rank

I don't know the regs on that, but, first impressions, it would seem rude to me. Then again I ETS'd in 99.

I just want to add my story. I received my orders for SPC (1993) via mail while on PCS leave from Korea. I pinned myself and reported to duty at Fort Hood, TX as a SPC. There were no issues with this but it got weird when my S1 (after maybe 6 months on Fort Hood) told me they had my promotion orders for PFC. I laughed said I'll show you my orders for SPC, I also explained my entire story. My initial enlistment contract in 1992 stated I was a PFC (college before enlisting). But somehow there was a mistake and for almost my entire first year in the Army my LES said E1 (yes I tried to fix in Basic and AIT). It was a good payday when it got fixed. it's an interesting story and I know too late to help but if you had orders pin if not wait.

I would NOT do this. Not as an E-5 at least. Now if you are being PAID as an E-5, I would show up with stripes period. Once yoau re paid for it, you're actually advanced.

Seme think kind of happened to me. My PCS order was transmitted just before I made SGT/E-5. When I arrived in Okinawa, a SP4 was my assigned sponsor and found me in Temporary Housing with my family. I was assigned to Field Station Sobe (ASA), but the main MP unit tried to claim me. The SP4 reported that I was a SGT and immediately, a SGT was assigned as my sponsor. Thing was, I was "pinned" at my last duty station (Walter Reed) a month before I went on leave.
When I reported in to Sobe with the SGT, the FIRST question was, "We need your promotion orders," so it was no problem. A bit different for you ... if you have your promotion orders, you CAN put your stripes on; BUT you might want to contact your gaininig unit's 1st Sergeant as a courtesy and let him advise you.
CONGRATULATIONS BY THE WAY.

Simple answer…. What contour orders say? Being promotable is not the same as being promoted.

I pinned myself MSG without the a formation or ceremony.

No you may not. You "made the list" just means you are eligible to be promoted. A commander cam still withhold promotion.
Further, your promotion is not official till you are pinned and you have the promotion warrant.
Putting the rank on yourself is invalid.

Let you new COC publicly promote you. Leaders love to promote their people and it is a great way to start your new posting.

As soon as I saw that I had been promoted I put the new rank on. Showed up to drill wearing the new rank and my 1sg was kinda bummed that he didn't get to pin me. Since you are going to a new command where no one knows you or cares enough (yet), I would say pin yourself and show up to the new unit with the new rank.

the first thing you need to do is verify it with your ERB and copy it so when you get to your Unit you can produce verification which is why every Soldier needs to keep is ERB updated and take care of all corrections. Your promotion will appear on your ERB.