First of all thank you for this nice hack.
I'm using it to add some additional ticket status definition to be used when ticket is still open (at present moment I defined 'active', 'suspended' and 'to be tested'). To do this I used Severity field, tweaked to "Working status".
I noticed that label tweak applies correctly when entering the ticket, but not elsewhere. For the case of reports it is not great problem, as it can be solved with an sql AS statement, but in other cases (i.e. the summary on the top of the ticket page) I still see old label 'Severity'.
It is not a serious problem, but if it could be solved I would really appreciate it.