Factory roof rails of an XS to fit an XT?

yes, those will fit.
They'll be quite the chore to install since you have to remove a lot of your interior panels to get to the mounting bolts.

Thanks for that info!
Wow. Yes that sounds complicated... But I imagine that someone at a subaru dealership might be able to manage?
I am in Mexico...

A dealership should be able to do it for you.
I know there was a how-to posted a while back about deleting the roof rails from an XT and installing the flush-mount rain gutters from an X model back when the SH-chassis first came around.

This would just be the opposite procedure, but the steps would essentially still be the same.

My situation is that I am in Mexico and having a very hard time finding used roof rails for the XT. I did find a B3 Tribeca 2009. By a any chance do you think the roof rails on that would fit my Forester?
Thanks for you help!