There any way to limit users from modifying their link descriptions with links from specific categories?

I know I can use templates to complete this task with if and else conditions

<% if category_name eq x cat%>description input form<%endif%>

but however, this is not secure since users can simply input their changes into the url strings instead.

They'll be able to modify descriptions from all links categories!

You'll probably have to over-ride the hook.