Basically you are doing two tasks here
1. Converting the disk to dynamic disk from basic, it is possible in windows when the FS is online
2. Add extra space 200GB once you convert the disk
For converting the disk to dynamic , refer the following article for more information and precautions
Change a Basic Disk into a Dynamic Disk
Once converted, if you have free space in the disk you may expand the volume, if you have space in another disk drive you can span the volume to add 200 GB from other disk.