I've used the panel line accent stuff over Tamiya's gloss clear without any issues. What I've found works is to apply it over the gloss coat and let it dry (12+ hours). Then I'd use a cotton swab dipped into enamel thinner, squeeze out most of the excess onto a paper towel so the cotton is barely damp, and then go over the model slowly removing any overwash. I don't spend a lot of time in one place. Instead, for those stubborn spots, I'll let the model sit for an hour and then go over it again with a new swab.
Note that Tamiya's paints (including their gloss clear) are acrylics and I've found enamel thinners generally don't affect it. Tamiya paints are thinned with X-20A thinner, which is alcohol based, from the smell. It's not the same as X-20, which is their enamel thinner. A lot of people get these two mixed up; X-20A is for their acrylics, X-20 is for their enamel paints. The paints that Tamiya exports to the US are all acrylics and should be thinned with X-20A. I don't believe Tamiya exports any of their enamel paints to the US, including the enamel thinner X-20. You can find it for sale at shops that import Japanese stuff, but not on Tamiya's USA website (tamiyausa.com).
The panel line washes are enamel based, that's why Tamiya tells you to use X-20 to clean up. I don't think X-20A will work at all; what it would do is melt the Tamiya paint under the wash and remove the wash that way, along with the paint, making a big mess.
The instructions for the panel line washes state explicitly to use X-20 to clean up, but they don't even export that to the USA. What I've used is Testors Enamel Thinner; it cleans the wash off Tamiya's gloss clear coat easily, without affecting the clear coat.