Ok, lets see if I am reading this right. The white tube is fasten to the s.s.aft tube, and the s.s. bow tube slides in and out of the white tube?
If that is correct, then this will be a permanent fix. I have this setup for my bimini, because to store it I need it longer, and to use it I need it shorter.
If you have the tools and are handy, you can buy the things you will need to do it yourself. If not a good marine canvas shop can do it for you. They should not charge you that much, because what they will use is left over things from other jobs. You will need a length of s.s. tubbing larger or smaller than the tubig you have, depending on your size. You will be replacing one of your tubes and transferring the end hardware to the new tube. In the smaller of the 2 tubes will be kind of a kob on the end of kind of a tension bar. There will be a hole drilled in the tube for the knob to stick out. And then at the desired length a hole drilled in the larger tube. When you have the tubes extended the little knob will fall in the hole of the larger pipe and lock it in place. To release it, you just push in the little knob. Easy fix, will last forever. 1 length of tubing and 1 little knob.