At least in the US, the rule is that you cannot descend below the assigned altitude until established on a published segment of the approach. And the ATC phraseology to back this up on every approach is "maintain XXXX feet until established, cleared for the..." I assume that the rest of the developed world is the same. (Am I right or wrong in this?) In your scenario, what segment are you established on?
"Established" doesn't mean LOC centered indication in FAA world.
First movement of the needle inbound is considered established as you have lateral guidance.
So GS capture with 1/2 scale deflection (or more) in APP logic would be perfectly feasible.