Hey - I know its been a month now - did you ever get this livery work done? If not, let me know - reply here, or send me a DM. I do livery work, and would be happy to do this for you - I'm sure we could figure something out.
First thing, though - and forgive me if you already know this part - when you see a livery that is truly "reflective" on a model...........that actually doesn't have much to do with the livery itself. The biggest part of a reflective livery is the model itself - the reflective aspect is actually a secondary "surface" texture layer built onto the model. Then, you just edit the regular livery to only have the parts you want/need to reflect - the rest remains transparent - and then use that revised livery layer as the reflective texture in the ytd. As i understand it (lol.......definitely only a very basic understanding!), that reflecitve texture surface layer on the model is slightly offset from the normal surface layer - and that offset allows the colours to be picked up twice, I guess? ......which somehow then creates that bright reflective look. It is a cool effect, for sure - but, again......something that has to be part of the main model build to start with. In a way, no different than some models aren't even built with a livery layer - if there is no "xx_sign_1" layer
But.......maybe you knew all that already! So, back to the question - do you have a model(s) in mind that already have a reflective texture layer? Then, this work could be done. If you aren't sure, just check the .ytd file in OpenIV - look for an extra "sign" texure - one would be the regular livery layer. If reflective, there will be another one that has "reflec" or something similar as part of the name.
Otherwise, another option is to create a pseudo-reflective look - using the 3M hexagon style grid pattern overlay on the parts you want "reflective". That doesn't really give a true bright reflectiion in game......but, it does make those decals have the look you would expect. I can send you example pictures of what I mean.
I'll stop now......let me know!