Guitar players - electric strings on an acoustic

[Cyclops]

Surely if the strings are tensioned turning the truss rod would be difficult. I've only done it once on an old Hoffner guitar but before doing it was told that you had to slacken the strings first.

This is partly correct: You only need to loosen guitar strings before adjusting the truss rod if you want to tighten the truss rod. This creates extra tension on the strings, which can cause problems. If you want to loosen your truss rod, you don’t need to loosen the strings.