Why did the Army change some of the MOS identifiers, IE 95B changed to 31B?

I think you mean the MOS structure. They changed some identifiers into MOS's as well.
The Army did a restructure around the time of the surge. The idea was to eliminate some redundancies and align branches. This aligned some of the enlisted MOS's to the officer MOS's as well. Now the overall structure is that the closer to 11, the closer to a combat MOS. That's an over simplication, of course. For instance, 94's became 67's which became 15's which are aviation. 11M & H were all combined into 11B. 91B, C and W all combined to become 68W combat medics. 68W ASIs like M6 and N9 became their own MOS's as well.

I know my MOS was 26B20 ASI K1 for weapon support radar repair with additional school to do the new (at that time) radars AN/TPQ36 / 37. That was signal corps while I was in.
Now, it lists as ordinance MOS 94M.

every few years the Army takes a look at their MOS rosters and does a overhaul, combining some, re numerating others, phase out a couple. just par for the course. When I enlisted there were 4 different Infantry specialties - 11B, 11C, 11H, 11M - they did away with the Hotels and Mikes, change Medics to 68W, and a whole bunch of others - don't sweat it mate.