If your final varnish is solvent/white spirit based, then there is some risk of reactivating the Mig enamel based products.
How long you allow the Mig stuff to cure before final varnishing might be a factor if you do decide to go this route.
I use an acrylic based varnish because it's safer on several levels; toxicity and risk of messing up my weathering. I always wait a couple of days after my last go at weathering to allow everything I've done so far a chance to dry, settle, cure, harden, react...