Yeah actually Ive done this before too and i always seal the bag.. another way I used to do is soak a sock... and throw seeds in there.. but there are disadvantages to the sock method.. and... actually the breathing in the bag is not pointless IMO because seeds like WARM, DARK, AND MOIST Places
"dank" if you will. Your breath is warm so it would do nothing but good IMO. Definitely wouldnt kill them.