I just killed one of my lash adjusters after revving the engine out too far..
Im unsure why, wether its related to my gas system or manual conversion or something else but the rev limiter did not exist to my suprise.. the dial went right up to 6k and I only hope no further..

Anyway I have some spare lifters/lash adjusters sitting around but some of them have come apart somewhat.. in the sense the piston has come out and while they can be pushed back together, I dont know how to relieve the pressure inside so they stay in place. Just wondering if theres any special way..

Get a small screw driver or a hole punch and lightly push the ball housing down in the middle while pushing it back into the casing, that'll relieve the pressure. Oil em up first.

Ive had no luck at all with this, could you clarify where you mean exactly?
Push down on the end where the rocker atm sits or push down on the side of the barrel?

I mean, compress the lifter and ball housing back together by lightly pushing the inside of the ball housing, then push back into the rocker arm.

If they wont stay then tape them up or use retaining clips