So I recently bought a damaged frame, which I plan on fixing and repainting. The decals are in excellent condition and I would like to save them if possible. I've read that you can heat decals with a hair dryer to remove them, but is there a good way to reapply them?

I doubt you will be able to remove them without damage. I would just order a new set.

I've given this subject some thought, as I have a "sticker" that is partially dislodged on my Mixte.

I have yet to try this, but I'm going to use some double sided (sticky) clear tape to refasten it. The tape I have is super thin (proly .003" - .006"), and I would assume work well with a decal too IF you can remove yours intact. A little X-ACTO or razor blade work in cutting the tape / decal outline should do it prior to re-affixing.

Thought about a tiny application of Super Glue (instead), but I think that might be too dicey and messy to achieve good results. There is a chance of destroying the decal (or sticker) or any surrounding paint work in the process.

I have one that was not a valuable frame to start with. The paint was bad but the decals were in good shape. I could not find any that were the same as the originals. Having new ones was not cost effective. So I stripped the frame but left the decals and was really careful around the edges. Then I taped the decals, primered and repainted with the original color. If you watch what you are doing there is no buildup line where the paint meets the tape. Be careful when removing the tape.

I then touched up the decals where needed. Because the decals did have a little patina, the end result was exactly what I was looking for. It looks like an extremely well preserved old bicycle instead of a brand spanking new one. It the blue one up against the fence.

https://s1110.photobucket.com/albums/h458/seypat/

It is very difficult to remove decals with out damaging them. Find good replacements and apply them carefully in the exact same spot.

3M Super 77 spray adhesive, if you can get the label off intact.

I have had some limited success in removing labels with a heat gun to soften the old adhesive. Some foil substrates will peel off but the old ink may crackle badly. Others will simply tear, so be aware that you may have to heat and pull, heat and pull, repeatedly. It can be laborious and frustrating. Small labels are much easier than large ones, btw.

With my Follis seat tube, I removed the art, but it tore in several places. I saved every scrap, sticking the pieces to a piece of archival white paper and reassembling it like a puzzle. Then I generated a high resolution scan of the flat decal and used that to recreate the original artwork. Thus, I wind up with the original sticker on a flat card, a digital scan that was necessarily touched up in Photoshop where the tears are located, and ultimately an Adobe Illustrator vector file from which I created a new water slide decal.

And yeah, what a PIA!

I'm thinking of doing this exact same thing to a couple of older bikes I have. I just wasn't sure it could be done and turn out alright.

Thanks for the advice guys. I will try to remove the decals and see how that goes before thinking about putting them back on.