I have a cactus that looks like an echinopsis (like a small barrel cactus) that I want to repot. Can I plant it deeper in the soil than it already is??

It is not a good idea to repot that type of cacti below the level it was originally planted. That rarely works well and usually leads to the plant rotting after it is watered. At least that has been my experience. It's also best not to water for the first two weeks after planting to allow any roots damaged during the potting process to regenerate.

I am curious as to the reason you might want to plant it deeper in the soil than it already is?

The reason I want to plant it deeper is because the bottom of the cactus is smaller in proportion to the rest of the plant. It seems to list to one side and I have put large rocks between the plant and the edge of the pot to keep it upright. Hopefully, as the plant grows larger, it will not fall over.

When you repot you can try leveling the plant by making the soil higher on the bottom of the pot on the side toward which it is listing. In other words, you are leveling it from the bottom of the pot while allowing it to remain the same at the top. I hope that makes sense.

You could also add a layer of gravel to the pot, so when the cactus is leaning, it is not touching wet soil.

Thanks. I'll try one or both.....

Let us know how it works out for you, Luke. Nice to see you here. Thanks for asking a question ... and welcome.