Galaxy wide role playing game

A ‘quite thick’ SF book I read at least 30 years ago in the UK, I can’t remember the cover.

The bits of plot I recall:-

Humanity has settled all over the galaxy and civilization is stagnating a bit. Most people, out of boredom, now take part in very realistic role playing.
They re-enact historical sieges and battles.(I think there may be mild hypnosis to convince them it’s real but I’m not 100% sure)

The protagonist is at some like French Musketeers battle with his rapier when he’s suddenly attacked by a guy in a suit of armour with a big sword. In full panic mode he gets a memory insight and yells "TIME OUT"

Everything freezes and a computer voice informs him he has five minutes to think of a solution, otherwise he will be returned to face his death.
He argues that the armour is incorrect and out of date for the time period, the computer informs him there is an actual historical precedence for this, somebody actually wore antique armour to sword fight in the time period, he was eventually shot at close quarters.

Protagonist is panicking now but suddenly a priority override signal arrives and his memory is fully restored, he is really a Galactic secret agent.
There is a problem somewhere that could endanger all life.

He is teamed up with a veteran combat engineer soldier and a girl agent (maybe more but I don’t remember) and they’re sent off to someplace that’s in a state of flux.

Upon landing the chaos catches them, I think protagonist becomes goblin like, the soldier has his hands turn into metal claws and his lower body becomes a metal screw for ground boring – I don’t remember how the girl was changed.

I think they then have a perilous journey and finally reach the place they need to resume control, other races have arrived also, a tiny constellation of microscopic stars that are a hive mind. Some man size frogs Whose main weapon is long sticks with sponges dripping with acid tied to the ends. Some robotic aliens with high tech and some Mongol type warriors on lizard back.

A big confusing brawl and the human team prevails and thus gains the "power/knowledge/force/control"

FURTHER MEMORIES UPDATE:-
At one point during the party’s trek through the chaotic environment they are captured by a barbarian tribe.
They incapacitate the soldier hybrid by hoisting him into the air and lowering his giant screw end into a cauldron/crucible of molten iron.

Then they let it cool off so he now has to drag himself along with a beach ball sized sphere at his base.
This was because, previously, he could very quickly drill himself underground and then (like Bugs Bunny failing to take take a left at Alberque) rapidly tunnel along sub surface.

I also am fairly (80% ish) sure that the galaxy en masse role game is called "Playing The Boards"