Welcome to the forum and congrats on the orange tractor.
Is there no shut off either at the tank itself or at the filter mount base????
On my little L175 there is a fuel shut off at the tank itself on the opposite side of the tractor from the filter. That is very practical for service but it sounds like Kubota did not maintain practicallity for all models.
Another way to deal with a service issue is to use a fuel line pinching tool. These tools are made specifically for pinching a rubber fuel line temporarily for a service procdure without any damage to the line. I have two varieties that I use for water and fuel lines in auto, marine and pretty much everything.
One quick easy way to make up a tool like this is to slide a piece of rubber hose over the jaws of some needle nose vise grips. By using the rubber pieces no damage will occur to the hose that is pinched off with the vise grips.
For long term service I would just put in a shut-off but for the quick and easy use a tool.
Good luck