Sharing the wealth… Maybe it’s been posted before. Apologies if it has.
Harness yourself to the wall of your condo’s or neighbor’s pool. I use some 4mm rope and an old climbing harness. Give enough length and basically paddle against the tension. It is kind of like a treadmill. It is boring, but with paddles you get a good workout.
I hit it before dawn to avoid putting on the show for tourists/neighbors.
Enjoy.
You can also use surgical tubing and make it a variable tension system. The faster you pull/stretch the cord the more resistance. The only caveat is you do slightly modify your stroke when pulling against resistance . Still many swim coaches this to build strength.
As for a normal rope I would imagine if as long as you are swimming at a moderate and controlled pace it shouldn’t have too large an impact on your technique. Certainly better than not swimming or swimming in a 10 foot pool 
I live in Hannibal, Missouri (Yes, the boyhood home of Mark Twain, Tom Sawyer, and Huck Finn) on the Mississippi River, so I just wade in, and swim north against the current. The biggest, most beautiful “endless pool” in America…