I heard you can just link your frame gun to frame bone 24 and then constrain it to frame right wrist. Is that true? And if it is, can I re-constrain it without getting this message?

That doesn't help. That's the tutorial I used to learn FP animation, and it's how I've been doing my animations already. I heard Donut say to link frame gun to frame bone 24 and then constrain it to frame right wrist (or the other way around)
Basically, I'm wondering if re-constraining will give me that above error message.

lol did you hear that from me? ill see if i can get icee to post too, since he uses this method, but look up a tutorial on keyframe based constraints. its amazing what you can do. you can constrain bones so they cannot bend more than a certain amount and cannot move without another bone moving.

you can constrain a model of the human skeletal system so it moves exactly like a real one (for example the leg cannot bend over the kneecap)

when i animate i link frame gun to frame bone 24, and then constrain both wrist controllers to frame gun. Sometimes though, it is appropriate to constrain them to a different node.