After a lot of disappointing experimentation with blending I finally lucked out and accidentally created a delicious espresso blend. This was only possible because I had roasted all three coffees extensively as SO, had grown tired of them and didn't mind using some on a punt, and needed something for a picky friend in a rush. I've now run out of one of the coffees (https://www.sweetmarias.com/el-salvador ... urbon.html) and I'm starting to realize why a good, consistent espresso blend makes for such dedicated followings.

Is it even possible to switch out coffees in blends like that? Or will I have to completely redo the proportions and origins? I'm relatively price insensitive, and I don't mind buying nicer coffees for a blend, but I also don't want to spend a bunch of money on coffees that don't fit my usual SO tastes and then also have them not work with my blend.

I don't think this is a precise science. If I were trying this, I would go to a greens supplier that describes its coffees well and try a coffee that seems comparable to your prior blend component. Tweak from there. I doubt you would be far off.

While we don't roast our own beans I'll often create blends with coffees that I otherwise don't prefer on their own. I will blend them with our favourite SO El Salvador in ratios depending on taste, experience and intuition. We often end up with concocted blends that are not only different from either coffee but also often better, interesting and a welcome change that even our 'regular' visitors notice immediately and enjoy.

This is most often done with coffees that are given to us as gifts that we would rather not drink on their own but don't want to waste by discarding.

It sounds like you struck a blend that worked well and ran out of the El Salvador bean. Unfortunately, unique origin, type of bean, altitude and other characteristics a certain bean has often changes the blend in ways that don't align with logic. But it is often said 80% flavor comes from the roast development for a certain bean. So if you can get another close match SO El Salvador and roast it to the same development, you likely could come pretty close to match your favorite blend. As Gary says, look at flavor notes. It may be possible to match with bean another central American country. I agree good blends are hard to find and duplicate. Good luck and let us know what you find.