Usually when I want to rearrange tiles quickly I'll open things up in Pyxel Edit, but it can't change tile sizes on the fly like yours, plus it's a little slower to move things around, so yeah, it's useful. It launched in windowed mode, but for some reason the x was greyed out and didn't work. I just tested it out a little, it seems to be a bug tied to the tile swap, since it works before I swap tiles but not after.
> Could you add a shift click for grabbing multiple tiles?
Done. Well, I went with simply click-drag to select a range of tiles. Let me know how it works for you, I thought it was slightly easier and more intuitive than a shift-click approach.
> I just tested it out a little, it seems to be a bug tied to the tile swap, since it works before I swap tiles but not after.
Did some testing, and I think this is the 'Window sometimes doesn't respond to clicks on title bar or window frame' issue that all my apps seems to have. I hate to point fingers, but I think it's something in SDL library that I use for display. I don't know what it is but it seems to get confused about whether the window is active or not. At some point I hope to do a deep-dive and figure out what is going on and hash out a solution.
In the meant time, try clicking off the window and then very specifically clicking back on the title bar area. That's usually enough to kick it back it shape for a bit.