Quote: " is there a way to do this ?"
Where the heck is Nickeydude with the unhelpful titles schpeel?
I love this title; it's almost like a "is this possible", and you already know my response, YES!
Quote: "I don't think vanilla FPSC can alter the player's life count."
Ply is right, there is no direct way to do it, but there is a work around.
Give the player excess lives at the start. (whatever you think the cap should be)
Then use any global variable for the player lives count, and display that as there lives instead of the real number.
So, in other words set the lives at ten or more or whatever but only start the variable at 3, and display that.
That way it appears as if we have only 3 lives and the player is none the wiser.
Then have a script that sets, reads, alters and displays the value of that variable running on the side.
If they pick up an extra life then just increment the variable.
Just decrement the variable once each time the player dies, and you are good to go.
Of course you would need to kill off the extra lives if they die three times and never get a extra life, but doing an endgame when the variable is at 0 is easy enough.
I'm not sure if I am making it clear enough, but it is doable in Vanilla with some creative scripting.