That's more the "hardcore" way:
You can move the large content/library folder to another drive and then create an NTFS junction at the original location. Windows and Fender Studio will still see the folder at its old path, while the actual files are stored on D:.
For example, after moving
C:\OldPath\Content → D:\Audio\Content
open PowerShell as Administrator and create the junction:
New-Item -ItemType Junction -Path "C:\OldPath\Content" -Target "D:\Audio\Content"
I would use this mainly for large sound/sample/library folders. I wouldn't simply move the entire Fender Studio installation or plugin installations this way, since those can also depend on registry entries, installers, services, etc.
Before deleting anything, first verify that the junction works and Fender Studio can access the content normally.
This also technically works for the standard VST3 folder (C:\Program Files\Common Files\VST3), while keeping the path expected by VST3 hosts intact. However, I'd only move that if it actually uses significant disk space. Usually the large sample/content libraries are where most of the space can be recovered.
Many plugins and virtual instruments allow you to specify or relocate their library/content folder directly in the plugin's settings or library manager. If that option is available, I would use it instead of a junction. Move the library to D: and then tell the plugin where its new location is.
NTFS junctions are particularly useful for software that insists on using a fixed path and doesn't provide an option to change it.
I'm planning to use NTFS junctions for ComfyUI as well. This way, when I update ComfyUI, I can easily make a small backup of the installation without also copying all the models. I can keep one central model folder and map it into the folder structure expected by ComfyUI and other AI applications.
So instead of having multiple copies, I only need one central folder containing the ~700 GB of .safetensors model files.