I have an open can of crushed tomatoes and all the other fixings for salsa. Can I make salsa from canned crushed tomatoes?

Yes, definitely! Just add other ingredients as you would for your standard recipe, maybe up the cilantro a bit to add freshness ....

absolutely... Drain the liquid
(you can use it for any gravy, don't have to waste it), In fact its waay more econimical to make salsa at home.

Yes! I do it often during the winter when I just have to have salsa, and winter tomatoes are just not up to the job.

Sure you can. Just be sure to drain the "juice" from the tomatoes before adding the other ingredients.

Yes, Salsa is pretty forgiving. It *might* be a bit watery..but you can adjust that by draining just a bit. Then adding your spices and flavors.

What is your application using it as a dip for chips? Because there are some other things you can do with base salsa recipe, where watery doesn't matter as much.
IE: Cook it down, with lime, garlic, peppers, add a shot of tequlia, finish with softened butter to make a sauce for cooked items or fish tacos.