You need to do both those things, plus something else.
Mario RPG uses the SA-1 chip, which contains an updated version of the lockout chip. If the SA-1 does not "see" a working US-type lockout chip in the console, it will refuse to work.
You need to make an adapter to fool the SA-1 chip. I have not tried doing this, but it should work. Email me if you want to try, and I will give details of which pins to connect. Basic instructions:
1. Get a spare universal adapter or converter that is designed to play Super Famicom games on a US SNES or vice versa. (That is, a simple extension adapter with no components inside.)
2. Get a spare US or Japanese game cart which uses the separate lockout chip (D411). 95%+ of carts use a separate chip.
3. Remove the lockout chip from the spare cart. Open up the adapter/converter and fit the chip inside. Of course the chip needs to be connected in the right way.
If you have a spare adapter/converter and US or Japanese game cart, I can try making this for you (for free). I don't have a spare adapter or cart here, so I have not tried this yet, but am 90% sure it will work.
-- Mark