https://forums.flightsimulator.com/t/new-ssd-m-2-nvme/570593/4?u=tenpatrol
https://forums.flightsimulator.com/t/msfs-drive-usage-workaround/641289/3?u=tenpatrol
If the company you’re renting the PC from allows hardware modifications (such as swapping or adding drives, changing BIOS settings, etc.), then technically you can install your own SSDs with Windows and MSFS.
However, please note that running your existing Windows installation on a rental machine - which likely has a different motherboard and CPU - will almost certainly cause your Windows activation to become invalid.
In short: yes, it’s possible if the rental provider allows hardware changes, but be prepared for Windows to lose its activation and you may need to reactivate it using a valid product key.