I don't know your pool volume nor how much water you use in backwashing, but I suspect it's less than 5% of the pool water volume each time. So that would reduce the borates by not more than 2.5 ppm so after a backwash this could be added, but it's not a big deal. I'd wait for at least 3 months and then test the borates level. You most likely will be able to go an entire season without having to adjust borates.
You don't need to worry about the borates over the winter, but if you have rain overflow that dilutes the water you may need to add more in spring upon opening.