The absolute maximum spec is just that - the maximum that a device can be subjected to - no safety factor here. The nominal 25KV spec that RCA specified for this TV should have some safety margin associated and 10% is not a bad estimate.
30KV is 20% over the nominal operating voltage of 25KV. Considering the date of manufacture of this TV, there were not many provisions for shielding the repairman or viewer from x-Rays. Consider the safety provisions of later years such as higher lead content of the tube envelopes and even lead shielded HV rectifiers and these are for TVs operating at 25KV.
If you continue to work on this TV or watch it in close proximity running at 30 KV, you may end up like Homer Simpson in post #5 of this stream:
http://www.videokarma.org/showthread.php?t=272531
No emotion here, just common sense.