Hm... Negative levels are pretty chunky... a +3? Maybe a +4?

*Checks SRD.* On the other hand, the Life-Drinker Axe is relatively cheap - if an effective 1 negative level in cross-balanced costs (i.e., 1NL to them = 1NL to you, which may well be a decidedly inaccurate comparison) clocks in at a mere +38kgp over and above the cost of a regular +1 Greataxe...

Certainly the object in it's original form would be well above the ratings for a +5 (hence why it's a +3 weapon that costs more than a +10 one, requires use of what is likely to be a cross-class skill for the primary users, and a fresh personal truename each use).

Hm... It would also depend a lot on the speed of the switch... for a 1 hour inscription speed, we're probably talking a... +3 ability? Hm... a little weak for a +3. Maybe drop it to a +2.