Can I replace a shimano tourney tz rd-tz50 rear derailleur with a Clarissa R derailleur ss.

Sure.
Will it work?
Depends on things like largest cog size, amount of chain wrap required.....

Chances are that if the bike came with a "Mountain" RDER, you need a "Mountain" RDER.

Maybe. The cable pull ratio will be the same, so if the Tourney worked with your shifters, the Claris should should mate with your shifters and index properly as well. But the 'SS' designation means you're talking about a short cage derailleur, which won't be able to handle big cogs on your cassette/freewheel or wide-range gearing like you might find on a bike equipped with a triple crankset.

To give you a definite answer, we'd need more information about your bike's gearing. How many speeds? Number of teeth on the big and small cogs? Single/double/triple crankset? How many teeth on the smallest and largest chainrings?

7 speeds
Sm cog 14
Leg cog 28
Triple crank set
Sm chainring 28
Leg chainring 49

The SS should work, but it lists the "largest" small cog at 13T.
That "shouldn't" be a big deal.

A Tourney AO-70 fits right where you want.

What does your Tourney derailleur look like?

There are two veriations: One has a hanger that attaches via a "claw" to the rear axle. The other has a bolt that attaches to a threaded hole that's suspended below your bike frame's dropout. Unless your derailleur is the latter, a Claris won't work without modification..

The shimano tz tourney is bolt on.