The critical opinion is how player-modifiable spawn interval helps execution, and people have reported 5 to 10 levels from the 240-level community pack where it's integral to the solution. When culture has grown over the design, the culture locks the design in place.
After a closer look, the following levels require RR-changes:
S19, C19, C30, D10, D19, V2, V7, V28, V29, H4, H12, H25, H31, H34
(and perhaps some more Hopeless levels that I haven't solved yet)
There are quire a few more, where it helps (sometimes depending on your solution):
S21, Q11, Q19, Q31, Q37, C5, C14, C17, C23, C27, C37, D4, D6, D13, D25, V9, V10, V17, V21, V25, H2, H16
To compare this with one-way arrows:...
But still there are several levels (e.g. Trading and Cooperation), where one-way-walls are created by specific terrain layouts. Other levels (e.g. Lix Cannon) had to be heavily modified to make up for the lack of one-way-walls. So there are ways to replace the function "one-way-wall" in the current version of Lix. But I see no similar replacement for the function "change RR".