Can I substitute full fat yogurt for ricotta in lasagna?

I wouldn’t do that... full fat cottage cheese would be a better option i think.

I haven't tried yogurt, but our beloved family lasagna recipe from before ricotta was available in our small town substitutes cottage cheese.

I would, I have, and I do!

There's no reason that you could not, but the flavor profile would be dramatically different. Might be a fun experiment to make a small batch with yogurt next time you make it traditionally and compare the too. I would definitely not serve it to an Italian. ;^)

I would not.