I’m not familiar with the msr tarp and poles so I don’t know what the differential is between your poles and eyelets (im presuming the’re eyelets ?), however just a suggestion. One way I’ve made adjustable poles (home-made cheapos) is to tie a small loop of cord and then tie a klemheist prusik knot around the pole, slide the prusik along pole to required length and peg out with a guyline and tent peg.
Poke the end of pole through the eyelet of tarp and the extra thickness of the cord around pole may possibly be enough to stop the eyelet slipping over it, and in any case when guyline is tensioned this will help stop it slipping down as well. You can use a variety of different prusik combinations and knots to achieve the same results if you get creative however for simplicity I have described and posted photos of an easy way (for example you can tie the prusik into the guyline itself and not have a separate short loop, or even use an icicle hitch which is very secure instead of a klemheist). Another alternative to washers which has no sharp edges to damage tarp is to maybe tie a turks head knot around pole, you may need to glue it in place though for added security if you can’t tie it tight enough not to slip, other perhaps better knots can be used for this too of course.
Cheapo adjustable pole, old tent poles joined with bungee cord and with a walking pole rubber on bottom to help stop it sinking into ground, fitted with klemheist loop for height adjustment, cost £0.00 as made from old bits and pieces, too thin poles will bend too easily.
