Since nowadays i'm doing some lower tunings lately i'm thinking of getting a 11 gauge. right now my guitar is set up with a 10 gauge by a guitar tech.

Do i need to adjust my truss rod or just leave it and change to a higher gauge?
Whenever you change tunings or string gauge always do a set up. Truss rod, bridge/saddle height, intonation etc. Unless you are doing a minor change in tuning like E standard to Eb standard or E standard to Drop D temporarily
well my guitar is not permanently in drop C or c tuning. but most of the time its in standard tuning. do i still need to set it up?
If you're switching between E standard and C standard you should probably set it up every time you change from one to the other and back again. Actually that's a pretty drastic change so you might want to invest in a second guitar solely for the C standard stuff.

Just for clarification's sake, when you say 'Drop C' are you dropping the 6th string from E to C and keeping strings 1-5 in E standard OR are you dropping strings 1-5 to i guess D standard and then dropping the 6th string past D to C to preserve the 'Drop D' tonal/harmonic relationships but bring everything lower in pitch?

Cause if your doing the first option I could see you possibly getting away with playing that version of Drop C on your E standard guitar without having to really worry about resetting up. If it's the second way then you can definitely not have to worry about resetting up things if you had a guitar dedicated to C standard.
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