HI Stephane,
I don’t use SP either, but that issue with the Texel Density seems like an issue of your Addon (ZenUV) (I am not familiar with that one, I rarely use 3rd party Addons).
If you change the Resolution of your Image (also known as Texel Density) in the UV Editor, that shouldn’t Scale your UV Islands.
Unless I completely misunderstand the problem.
