I know what you want to do, but unfortunately you can't do it.

What you want it's something like
MakePORTB CON PORTB & %00111110

but this will not compile. What you may do is use a Macro, but there's no advantage in this case.

btn_x = PORTB & %00111110
Work, but only where it is called.

You may use A timer interrupt to refresh btn_x, but still, there's no real advantages, and you also need another variable to confirm that btn_x have been refreshed.

Assuming you want to poll some push buttons, then yes Timer interrupt could be interesting. That's how I deal with them most of the time.

You can use the timer interrupt to read the push buttons, to confirm that it's not just a glitch and then, to do the debouncing. Now we talk