Has anyone modified a startrite352 upper guide/guard adjustment?

[Lons]

On the contrary, if the OP’s saw is working as designed (and that design is not unique to his saw), then there may well be something (seriously) amiss that should be addressed before looking at potential refinements to a system that, by design, does what is intended and required.

Well on my 352 which by the sound of it is of similar vintage to the OP's saw the mechanism is so simple there is very little to go wrong apart from loose nuts or excessive wear both of which would be pretty obvious and not difficult to correct. None of us know of course how competent or otherwise the OP is but I suspect he's practical enough.
I'm in full agreement that potential faults must be addressed before refinements but it is possible that he's just fussier than users like me and just wants a more refined mechanism, there may well be nothing at all wrong with the saw, no-one who owns an old 352 would say the machine is sophisticated.

We're all just guessing, a few photos to show what's happening would make it much easier for us to make informed comments.