Yes it's possible to mix assembler. you just need to use ASM/ENDASM
Code:
	ASM
	' your asm code goes here
	ENDASM
Unless you define your variable as SYSTEM var, your PBP variable must have an underscore before them
Code:
	YourVar VAR BYTE

	ASM
	' your asm code goes here
	CLRF _YourVar
	ENDASM
And PBP don't appreciate BANKSEL. you must use CHK?RP instead