Yes, no, maybe, it depends
Lots of variables makes this tough to answer. ANG C-130s are about the most prolific units out there, so easier to change units. Fighter to heavy, somewhat easy, if the gaining unit wants/needs you. Heavy to fighter, not likely. Heavy to heavy, easy if the gaining units wants you, needs you, and has the funds to get you a school slot for the new airplane, if you are doing something like C-130 to C-17, KC-135, KC-46, etc. The ANG is sending a few folks from heavy units through the T-38 track again, and they had not done that since about 2000. I think that is to have a few hometown guys able to fly a fighter/attack aircraft/UAS in case the unit ever changes missions, not for some plan to have a dedicated heavy to fighter cross flow. The ANG is a bit more politically connected and congressman seem to fight a bit to keep units alive and kicking with a flying mission than AFRES who generally does whatever big AF says.
Units also understand that things happen in people's lives. So years down the road, if you get hired at company X next door to AFRC or ANG unit Y, and you are killing yourself getting to the unit on your own dime and killing your family time, they should support and help you make a change. Because ultimately this is a volunteer force and it would be better for the taxpayers if you were able to stay in the service rather than walk away after your initial commitment because the demands of service were too demanding.
A traditional guardsmen/reservist has a three legged stool of life to balance, family, civilian employer, and military. There are those who will say that is what you are doing is keeping a balance of all three. This means trying to spread the anger around and the best you can do is tie and have all three entities equally mad at you. In other words, the family is mad because you are gone to either the civilian job too much and the squadron too much, the civilian boss is mad because you deploy too much, the squadron is mad because you did not volunteer enough for deployments. Others ( I included) will say your holy trinity of priorities is family, civilian employer, and the military. That changes the anger matrix a little bit, so for me, the family always wins and must be the most happy of the three, so that means sometimes I spend more time at the civilian job and less at the squadron, and then sometimes it is the other way around. Are there ways to mitigate this? Sure !! Always try to live with one of your jobs and not double commute. Pros and Cons to living either place. Live with civilian job and the military pays for your place to stay when you are on duty. Live with military job and use military leave to adjust your schedule and be home when you need to be, but you might be in a crash pad at the airline, if your trips are not commutable. Thats a whole different thread and years away from where you are now.
Bottom line. Pick the units near where you live, work, go to school that fly aircraft with missions you think you might like. If there aren't any or you aren't getting positive feed back, then cast a wider net. Make phone calls, go visit, then apply and cross your fingers. If you only get one chance, take it, focus on being the best you can be at training and in in follow on aircraft and adjust your plan down the road. If you get multiple selections, then evaluate based on the best information you have available, then focus on being the best you can at training and in follow on aircraft and adjust your plan down the road when life happens.