No problem boss. Even if you don't use GURPS as your system, it's a Generally Useful Role Playing Supplement.
And what do you mean by combat system design?
For combat styles there's the Martial Arts supplement.
But for changing how the system works....
Like, GURPS is HEAVILY simulationist, down to the stats, so trying to divorce from that is tricky as fuck.
As a result of being simulationist it's also really really deadly, you know, like real life is.
However, speaking as someone who has been playing with GURPS for more than a decade you can weld a new system on top of the basic one, and play around, so long as you keep to one second steps.
Here's combat examples from GURPS
themook.net/rpg/examples/
Keep in mind I haven't extensively play tested this, but here's an alternat version I cooked up a while ago.
Players are moving around a 'circle' of 16 spots, they can move 1 forward for every .25 to their speed (normal person has speed 5, average combatant is 6-7)
Once they complete their circle they get actions equal to 1/2 their speed rounded down, but not all at once (usually).
So Bob completes his circuit and has 3 actions because he has speed 6.50. He readies his axe because it was unbalanced from his last swing.
Everyone moves forward on the wheel, this isn't a hassle and so goes fast.
Bob closes the distance
Everyone moves, George completes his circuit, he has 2 actions because his speed if 5.25. He can do a flying tackle of George and Renegade Interrupt.
Roll the combat. Bob and George start the circuit again.