Paint type Identification and blending

[mini_surfari]

We've recently picked up a 'refurb' project rather than full resto,

Over all the paint work is very good (full respray about 6 years ago I believe), however it has had some grp 4 arches put on at some point. The plan is to weld up the extra holes and paint just the areas around the arch.

Is there any sure fire way to tell what paint was previously used (2k etc)? Does cellulose thinners have much effect on 2k direct gloss for example? And then from there I can work out the best way to blend it.

Cheers, Oli