So on the first without LUA... idk maybe not, with Lua definitely, only a matter of what you want to do and what trigger fits what you're trying to accomplish. Post in LUA Legion area about the specifics and I'm sure you'll get pointed in the right direction.
On the second when it comes to setting ship fuel via gui, you can't.
However attached is a script, copy\paste the contents of SA_RefuelSelectedUnitsAskUser.lua into a Special Action, call it whatever you want and mark it active and repeatable, let you scenario editor environment move forward for ~1 second, the Special Action icon should appear, if was not already available.
To use, select any number of ships, grouped or not doesn't matter and then run the special action.
You will be shown the current contents of the ship's fuel stores, there can be more than 1.
Enter the type number you want to change.
Enter the amount you want that type set too.
..if you selected more than 1 unit it will repeat this process for each of them.
..if you hit cancel or a clearly invalid number or entry like not a number etc.. that unit will be skipped and you'll have to select it again and try again:
When it's done you should get a count of how many it actually touched (ie skipped are not counted).
Downsides at the moment is you can only change 1 type per unit at a time. Sorry I threw this together pretty fast.
You can also select aircraft, but if has more than 1 drop tank I skip it to avoid a problem, use the gui instead for those. I included another in the zip that refuels anything you select to max on all types, in case you need it as well, or if not no harm done.