Template Variables only in a specific section

Hello,
sorry for a newbish question, but I failed with searching.

Whole my site uses the only template (though it’s controlled by phX conditions). There are several sections with documents, one of them belongs to a certain document group. I have a template variable set to this document group, but the problem is, I can still edit the template variable value while editing other documents which don’t belong this specific document group. This confuses my editors

How to make TV disappear for these other groups?

Thanks in advance.

Create a duplicate template and have it be the only one the TV is assigned to...