Plan to cut two new registers into the main trunk line running thru
the basement to add heat to the room. Current registers in that room
are "off-line". Trunk runs in the ceiling, behind plaster. I plan to
cut the hole, fabricate a short duct, put the register in the ceiling,
right off the trunk. Seems rather simple and straightforward.

(just in case) What am I forgetting?

Thanx
Renata