I have replaced the water valve on my previous, older 2010 North Trail 31 BDSS, RV without removing the toilet. It was a bit of a pain but can be done if you have enough clearance behind to get your hands in to remove the valve.
On the other hand, The toilet valve replacement kit that I used contained a replacement toilet seal and the toilet is only bolted down using two bolts so it may not be that much of an issue to pull the toilet and replace the valve and toilet seal.
Either way, you still will need enough clearance to remove the waterline from the valve. If you have enough clearance to disconnect the waterline at the valve, you probably have enough clearance to replace the valve.
It is not hard to replace. Not sure why your valve is leaking but make sure to fully winterize your valve to prevent this issue from occurring in cold weather during storage.
Here is the link to Thetford Aqua-Magic V water moduler service kit instructions.
http://www.thetford.com/wp-content/uploads/2015/02/Service-Kit-31705-Water-Module.pdf
The retaining screw is accessible from the underside, Head of screw facing floor, and can be undone once the waterline it disconnected from the water module.
The locking tab and remaining instructions are pretty straight forward and relatively easy to do. You may want to use a small mirror to visually locate the screw and locking tab etc either before or as you work. You can also use the replacement module as a reference if you cannot see exactly what your doing.