It is common practice to reduce RPM after take off for noise abatement. 2500 RPM is a common choice, and then maintain full throttle throughout the climb.
This should not result in an 'overboost' otherwise fixed pitch props wouldn't be possible (29" and 2300 rpm is typical of FP at take-off).
However normal practice would be throttle-prop-mixture when decreasing power and mixture-prop-throttle for increasing. The only difference is that there is no need to throttle back when decreasing RPM in the climb.