Have a down bag that needs some refilling in the hood area. Have an old down parka that is the down donor. How do I transfer the down from one to the other effectively, without making a mess. Also, I am just planning on making a small slit in the hood section on my bag to fill and resew the hole. Is this the best way, just carefully cut and sew? Any tips would be appreciated.

you need a small space with no draughts and no fabrics that feathers will stick to. If you do not have such a space in your house can you erect your tent inside? Clean the space you decide on carefully and fully before you start so you can pick up escaped down and it will still be clean. Have a vacuum cleaner ready to pick up down before you open the little space.
When you do it you must move very slowly as even with no air movement fast movement will move feathers about.
I assume you will unpick a seam of your hood for a generous hand/fist width. Static is your enemy, example: dont store down in plastic bags paper bags are better

"How do I transfer the down from one to the other effectively, without making a mess"

tape a small piece of nylon mesh or panty hose (or a sock) over the end of your vaccuum cleaner hose. suck up wads of down from the parka - usually this will be a small handfull, good for shoving into that hole.

of course if you have a workable seam, use it. (instead of cutting holes)
mike

Does the vacuum damage the down? And are you talking about netting on the end of the wand, or the hose, where the wand fills?

I have moved down by hand several times. The best spot is in a small bathroom. I cover my hands with climbers chalk, so the down does not stick. Sure a few feathers float around, but just pick them up. You should not need that much for a collar. Got an old pillow? Just do it. It is not difficult.