I'd appreciate if you can explain your setup. On my PS3 debug updates is enabled, but how would it help prevent accidental update (from a original disc assuming one becomes available in future versioned 4.80), or somebody doing an update via USB in my absence?9.99 spoof on qa flagged ps3 is still doing something. In case that sony release higher firmware you not will be prompted to update because you have already higher firmware. But anyway, manual update is still possible.
You should enable debug updates, and try XMB lock, plus 9.99 spoof. I think is enough.