Well....let me try to answer your questions with facts.
To be a RSAF pilot - of any kind, you need to be either Pes A/B.
Cause afterall they're combat commissioned officers, got to be
reasonably fit. In case you eject and gotta try to survive in
hostile territory, you also need to pass your IPPT and able to
qualify for OCS.
Yes, there're many ex-RSAF pilots in SIA. They even have a
scheme to help them transition over. There's no such thing as 'more
dangerous'. Every plane has their handling limits. An airliner
can't manoevre like a fighter and it can't overspeed, if not it
will disintegrate and breakup in the air. Airline pilots have to be
type-qualified to each type of aircraft and be 'licensed'. Military
pilots need to go for training and type-qualification.
No, I don't think a fighter pilot can just takeover an airliner and
fly it just like that. The visual cues, systems etc. are very
different. They can probably 'fly' it like, can control the stick
and throttle, operate the ILS, but things like landing etc. have
delicate and specific settings.
In the US, they're more proud of their military rank and
in-flight announcements sometimes they will even tell you they're
reserve of ANG pilots.