The 'Refuel' signal: If this signal is found in the station name, the train will skip over the station if it has enough fuel.

what exactly does it mean: enough fuel?
A some static minimal fuel level value or percent? or is it based on a next station distance from current location?
Can we modify/set this fuel value?

never-mind.

Just info for others - the logic is the following:
1. If there is more than one fuel cell, then we check the second cell: if it is empty, a re-fuel is required.
2. if only one fuel cell inventory is there, and it is empty -> re-fuel
3. if it is not empty, and it is less than 25% of stack - re-fuel.

You know this from the code I suppose? Can't catch 2-3 cases, are there some mods which change train fuel cells count?

yes, it depends on the code.
just played with my own prototypes

Just info for others - the logic is the following...

Thx man, great work!