file 485 at first
after 485 has been pending for 180 days, feel free to change.
If you want to change right after 485 is filed, make sure your current employer doesn't withdraw I140. If the current employer doesn't withdraw I140, you can change right away with H1 transfer. Then after 180 days, I485 can be transferred.
The above is LC-based.
If it's NIW, not a problem at all.