Use the tense that explains what's being done. It's not fun but that's a sign that there's work to be done.
If it's NEW functionality, then use the imperative. If you CHANGED functionality then use the declarative.
Just use the grammatical rules of ENGLISH -- specifically tense -- so in that way you can be sure that it all makes sense.
-- edit -- and apparently I've been watching way too much ERB and PRB on Youtube.