So you identified the problem in the 5 meter long section at the southern end of the street, where the sidewalk geometry has already merged into the street, but is still tagged "sidewalk=separate" and "foot=optional_sidepath"? Then it would be appropriate to split the street line at this point, not to falsify the tags along the entire road section.

Your change had no added value for the routing imho, as no "use_sidepath" was used here. But even if using "use_sidepath", a router that assumes a general ban instead of a strong penalty for such short sections should considered to be broken (there is currently a discussion about this in the community forum).

With your change from sidewalk:right="separate" to "yes", on the other hand, you have effectively introduced a second sidewalk or duplicated data, which is definitely wrong.

Regarding "optional_sidepath", of course thats an uncommon tag, but it seems to make sense to me here, as the street is a "living_street", so you can walk there, but there is also an optional sidewalk. In the bicycle context, "optional_sidepath" is often used in such situations, so it is logical to use it for pedestrian traffic as well (even if this situation rarely occurs).

(Sorry for the harsh discussion, but I am more and more annoyed that remote mappers often edit already very detailed data with supposedly good intentions, but make it worse in the process.)