No adjustment at the registers? You can get better registers, then avoid introducing penetrations and possible leakage points. Sounds like you have tight ducts, and youll want to keep it that way.
Hmmm... I'll take that into consideration... don't want to run the risk of messing with already "tight ducts". I did install new Hart & Cooley registers and adjusted them down quite a bit. Amazingly, that did send more air to the back of the house and lowered the front to back delta to about 2*. But you can still hear the air coming from the registers when you're in the 2 b/r's closest to the plenum, whereas the other registers in the house are virtually silent. I was hoping dampers would silence these registers and allow them to be opened all the way. I suppose I could have FPL do another duct leak test for $30 after the dampers are installed, and if they leak too much, have FPL insist that the contractor re-seal at his expense. Most installers are also on the FPL PIC list for duct sealing and I'm guessing they don't like customers complaining about their work to FPL.
Is there any ill-effect on the equipment by restricting airflow at the register?
The only Ill effect I could see is if the ductwork is marginal to begin with. Equipment needs 400CFM per ton and efficiency suffers if it isn't there. Closing close registers raises the overall static pressure and reduces CFM and/or will make a variable speed blower work harder. Smaller equipment requires less ductwork/airflow and closing registers will have less of an effect.