Any easy fixes

my Dad used a couple strong 1-1/2" - 2" round magnets for the sagging headliner in his 91 dynasty after the dealer couldnt make it "stay fixed"

Toothpicks, that's what I used on a 88 shadow till I pulled it out and reglued it with spray adhesive, just break the ends off or watch your head while getting in and out.

T-headed fabric pins
are a temporary fix,
and are a little better than ordinary pins as the T presses the headliner upwards over a wider area.

If the headliner is sagging at front or rear this works without looking too bad as the sun shades will hide the heads,
but you can use the T-pins in the middle areas too, and it might even be possible to paint the heads to match the headliner color.

Wall Mart usually stocks them where fabrics are.

stitch it!