No problem at all. register as a hobby flier, put your (pilot, not aircraft) registration number on the bird and enjoy. If/when you take the Part 107 test, you get a license number and then register your bird with a unique number. Think drivers license and car tags. Take the old registration off and put the new one on and you're ready to go. And yes, you can still fly as a hobby flier with the bird.
Absolutely no problem as long as it is for hobby. That is how I started. But, when you get 107 and want to make a little [emoji385][emoji385], then you need to reregister as commercial. That is what I was told and did. That $5 to reregister as commercial was made up with the 1st commercial flight I did! [emoji6]