I'm remodeling my basement and plan to replace all of the interior doors with molded 6-panels. Unfortunately none of the rough openings are standard height due to "creative" HVAC ducting and support beams. I cannot modify these ROs. I'm dealing with 76 1/2" RO height. I would have to trim around 6" from the bottom of the jamb and door to make a standard pre-hung 30"x80" door fit. Is that too much to chop off a molded door, even if it's the "solid" core version (e.g. Masonite SafeNSound)? I know I would also need to find doors without pre-drilled knob holes so they wouldn't be too low after cutting.
If I order "custom" sized doors, would the manufacturer be doing the exact same thing I'm doing and just replacing the bottom rail for integrity? I'm doubting they actually modify the mold and panel placement. If so, I'd rather just do the cuts myself and spare the custom cost. Any info is appreciated!