>>8555664Primers and thinners are entirely different things. All paints, primers and regular ones, consist of pigments, binding agent and a thinner. (Varnishes are much the same, but with clear or no pigment.) Now that thinner is what may harm the underlying layer by starting to dissolve it, that's why I talked so much about it.
As for Mr Thinner, if you mean Mr Color Thinner then that's good stuff and should for obvious reason be entirely compatible with Mr Color lacquer paints. If you mean MRP's Mr Thinner then I haven't really heard anything about it, but their paints are good stuff so they should know what they're doing, but compatibility with other brands of paint is merely highly likely rather than guaranteed.
For what it's owrth, I use Mr Color Levelling Thinner to thin both MRP lacquer paints and Tamiya's acrylics with good results. Aqueous Mr Color worked too, but not quite as well, gotta try their own acrylic thinner there to see if it was the thinner or if it's the paint that just doesn't play along any better than that.
Here I should probably point out that there's both Mr Color (Gunze/Creos) and Mr Paint (MRP). Two completely different brands from different makers. Confusion may ensure.