Slightly the worse for wear today, so after a day at work having to use my brain, I decided to have an evening doing non-brain-strainy stuff.
I have (as commented on Twitter yesterday) some laser decal paper. This has the advantage over inkjet that laser printer ink is waterproof, so you don't have to spray the printed decals with acrylic spray before you apply them. Also, I happen to be the happy owner of an A3 colour laser printer, - a parting gift from IT at my last job - it had been sat in a pallet outside the tech office for 3 years unopened, and we were shutting the company down… The downside is the colours are a little less vibrant than with an inkjet, but that's a small price to pay for a heck of a lot less faff.
They're a little more fragile than ... Actually, thinking about it? I strongly suspect the custom decal folks in our hobby use laser-printed paper, so that may not be the case :D I am aware that (after some playing) you need to make sure the surface you're applying is smooth (ideally spray gloss varnished) and dry (patience!), and also not to remove the decal from the water too early, in case not all of it lifts.
You are also going to have to cut around your design fairly carefully, and you need to re-gloss varnish afterwards before you apply your final sealant coat. I haven't tried using MicroSol and MicroSet, but I suspect these or Humbrol DecalFix would also help.
Either way, these have come out pretty well....