Here is a simple houserule.
When considering a change of career, the player may choose to "stay" in the present career for another Rank by paying the normal career change cost. If he does so, the GM must still provide a new character sheet with a blank career advancement section.
The obligation to change careers to get better was one of the things that bugged me in previous versions. The wonderfully flavourful and diverse basic careers would quickly disappear as the PCs moved into advanced careers. Hunters were necessarily less tough and agile than scouts...
Now, with this houserule, V3 will allow for extremely competent and experienced hunters ! Or anything for that matter. That makes every career an advanced career of sorts.