OK, sorry, I misread "My question is, would it hurt to pinch the rocker return line closed?"
But, my advice was/is still correct.
Pinching the "return side/line of the fitting" would serve no purpose with fittings with sealed "return line/side", depending on what you mean by "return line" or "return side".
Such as the fitting shown below, left (59-63 rocker arm assembly).
The fitting shown below right could be pinched (or, the "window" could be closed).
Which year/type connector do you have (see link in above post)?
