man, i havent replaced fluid with fork still installed in a long time.
Not difficult at all if you use a small funnel or a syringe attached to a flexible hose and you have the 105 cc of ATF measured in a cup ready to pour. If the bike is on the side stand with the upper fork cap undone and 2-3 spring coils exposed, you have the space to do it with minimal mess.
Just insert the flexile hose between the spring coils and pour the fluid. Then place the bike on the center stand; the exposed spring will drop into the fork tube and the cap threads can be engaged and the cap .can be fully installed.
Repeat the same operation for the other fork. This is how I have changed the fluid on my 350F.
However, if the OP wants to fully dismantle the fork, then it is easier to do fully remove the legs and do that in a bench vise.