Testing into a new sub-caste...

[Tegyrius]

Is this found in the warrior caste of any clan other than the Ghost Bears?

(I'm trying to align the fluff for a custom design that's on my whiteboard.)

[AlphaMirage]

I suppose it's possible to go up a level although it seems like mostly falling from one to another. 

Warrior to Tech or Scientist (or Laborer for Elementals) though I suppose Laborer to Merchant or Tech is possible as well.  We don't see much of the Clans other castes except when the Scientists go nuts during the Reading.

[Tegyrius]

I was specifically thinking of the Ghost Bear system for testing from, say, MechWarrior to Elemental. Getting a second Trial of Position.

[Natasha Kerensky]

I could have sworn the Bears can test down to become tankers like the Horses, but I can't find the reference.

[Vition2]

I always got the impression that this was standard practice in most clans, but those it is specifically called out in make more or better use of it.  I figure most of it goes something along the lines of

1) Trial of position for a combat cluster position
2) Trial of position for non-combat cluster position (guard duty, police, etc. - potentially even PBI in a combat cluster)
3) Trial of position for a civilian position
4) You are a failure, become a laborer

Any of the first two could, and probably often do, result in the death of the potential warrior.  Those clans which are specifically called out to allow for secondary trials are for other combat cluster positions, a MW or ASF pilot could become a battle armored warrior, or a tanker could become tanker crew, etc.

I don't have any fluff to back any of this up, but this is kind of how I see the clans working.

[Archangel]

I always got the impression that this was standard practice in most clans, but those it is specifically called out in make more or better use of it.I don't have any fluff to back any of this up, but this is kind of how I see the clans working.

Most clans didn't for the simple fact that they didn't deploy conventional forces in significant enough numbers in their toumans for it to matter and those that did were forgotten by their leaders most of the time ('Real warriors' don't consider members of the Watch or police to be 'true' warriors  ;)).

[Minchandre]

Hell's Horses can "test down" - i.e., vehicles or conventional infantry, if they fail their trial.
Ghost Bears can retest as any other subcaste (even of equal prestige); e.g., 'MechWarrior to Aerospace Pilot
Steel Vipers can retest as conventional infantry only.

EDIT: Also, ProtoMech pilots are drawn from washout Aerospace Pilots, though I don't know if it's been said that it's only from those who fail their final Trial.

[Archangel]

EDIT: Also, ProtoMech pilots are drawn from washout Aerospace Pilots, though I don't know if it's been said that it's only from those who fail their final Trial.

It depends at what point during the development of the ProtoMech.  Initially only washouts were used as Clans were testing the technology, but later entire aerospace sibkos were being reassigned as a whole before they even took their initial Trial of Position and finally some Clans started designing/creating ProtoMech pilot sibkos.