Is it worth it to change the MOS 42A to 25M?

First drawback is that it's difficult to find class seats. Not impossible, but by the time one becomes available, chances are the MOS will go over strength or you will be getting promoted. Promotions are very slow compared to 42A. 42A has great promotions to SSG and almost 100% pickup rate for Warrant. Promotions slow down to E7-E9, but with some work and patience, you can reliably make E7 or E8 before 20 years. There are also civilian HR certificates you will be eligible to apply for after several years of HR.
If your goal is to be a graphic designer when you retire, then 25M would allow you to gain some experience and maybe even moonlight doing graphic design while on active duty.

As for retirement, you'll make enough money in your pension that you can do whatever you like as long as you work. You probably won't even work in your MOS field when you retire. Twenty years down the road you will have experienced a lot of new career opportunities, many that you've never even heard of. So, figure out what you could see yourself doing for the next 15-20 years and do that. You got 42A with great career progression and assignments everywhere in the world, and you have 25M with poor assignment choices and progression but in a field you are already interested in. You just have to figure out which is more important to you.

As a 25M, promotions are slow and PCS moves are limited. There's a 90% chance you will be assigned to a PSYOP unit at Bragg and sometimes to a SF group.

You will deploy with the Spec Ops Soldiers. Rotations can be between 3 to 9 months. Depending on the BN you are assigned too, you will will support COCOM which supports and focuses on a region, for example SOUTHCOM focuses on South America. So they go on missions to Columbia, Peru, etc.

Hopefully, this helps. I have no complaints about the MOS and fast tracked through the ranks with some effort. Good luck.

To be honest Graphic Artists are a dime a dozen worldwide... I pay about $10 per job in India Bangladesh using Fiverr. Many have Master's degrees.... Follow your heart... I'd rather create than eat donuts, keyboard and BS.