I'm thinking about putting an EQ-pad inside the kick of a 70s Ludwig. It stay there with 2 velcro strips. Do you think the adhesive can damage the outer ply if I ever want to remove it?

thx!

It won't affect your inner shell in any meaningful way.
I say do it and don't worry about it.

It might pull some of the finish off if you ever remove it, but it might not. Using a hair drier to heat the velcro, thus softening the adhesive followed by some mineral spirits to remove any residue will probably prevent any damage to the finish. If you are ok with the risk then do it. If not you could make some metal tabs to install under the lug screws in the areas that you need the velcro so they could be removed if you ever need to remove the velcro.

If the drums are completely mint, then I personally would go the tab route. If they aren't then just stick them to the shell.

It's a good idea to heat the adhesive if I ever want to remove it without damage. thx

Just use sew-on Velcro and capture it under the lug screws.

Fully reversible and zero damage, or chance for damage.