You can resize the Windows partition, and it will still boot. Windows will give an error at start-up the first time, saying the disk size doesn’t match its records; it will run
checkdisk and update its records, and then work fine. I’ve done this many times.
You cannot move the Windows partition though, or it won’t boot. It’s worth pointing out that if you shrink from the left side of the Windows partition, what you are actually doing is shrinking, and then moving; ONLY shrink from the right side of the partition. You also should not expand the partition on the left side, as again you’re actually moving it to the left, and then expanding off the end; ONLY expand from the right side of the partition.
I would also point out that partitioning is never a 100% safe activity. You are altering the partition table; if that fails (slim chance) your entire disk is at risk for data loss. It’s always a good idea to have a backup of your entire drive before engaging into any form of partitioning, not that most people actually do it.
Windows can shrink its partitions, too, so why not go with that?
Simply open Disk Management, right-click on the partition you want to resize and fire away. Safety guaranteed.
If you find the space you can gain to be too small, you could defragment the partition (even if it’s on a SSD). Don’t expect too much, though, there are many immovable elements on a partition.
You should have no issues with Gnome Partition Editor and resizing Windows partitions. I have used in countless times with no issues.
Resizing the boot partition with an external editor (for example GParted) doesn’t appear to work for non-NT versions of Windows. Booting will cause an unspecified error on my ancient Windows 98SE virtual machine.
I just used GParted to reduce my Windows a further ~100GB more then Windows Partition Manager would. I carefully watched the process, and it moved over 30GBs in the process.
It worked without a hitch: it’s a very smart program. I now trust it. It ended up leaving Windows with less than 1% usable space! Which is great because i could get into Windows 10 and remove over 30% of the stuff, which makes it run better. But be careful.
This fact points out that GParted awesomely moved all the files in the NTFS folder to a tight nit space, and …
I saw it smartly checking for boot loading ability, and checkdisk as well for Windows. Brilliant.