I've seen some people with the pin-pen merger say on forums that when they try to speak without the merger that they make hypercorrections like lowering the first vowel in "minutes" when saying "ten minutes".
I have the merger, however I can speak without it without making any hypercorrections usually. Spelling is typically a good guide as to what words use what pronunciation in nonmerged speech. There's a few words like "friend" and "English" however.