It's possible. I've done it at work before. Always make a data backup before doing so though, as you never know
Use MBR2GPT.EXE to convert a disk from the Master Boot Record (MBR) to the GUID Partition Table (GPT) partition style without modifying or deleting data on the disk.
learn.microsoft.com
Slight update: i did it using option 4 in the windows club article, but i think option 1 will likely be your easiest bet
Double update: though im not sure how safe the data is in option 1? The article specifies without data loss, so it should be ok I think. When I did option 4 it didn't mess with data from what I remembered. But always always always backup data when doing something that invokes your data or windows install like this. Better safe than sorry.
As much as I shit on OneDrive, it does a decent enough job of backing stuff up for me.