I'm currently testing out a rule where any of the players can choose another class and take one rank in that. This "normal" class removes the 8th rank instead of skipping a rank, like the more special advance-schemes. This is only for skills and talents and all at GM's approval. They don't gain the special ability of the new class either.

Example: Arch-militant with 3 ranks, just gaining the 4th rank and choose Missionary and get that one at rank 1. Added together the character is rank 4, and is a very devout soldier.

This makes the characters a bit more diverse, and I don't see any problems with game-balance when only allowing rank 1. Of course, psyker + navigator would be a no, but psyker + seneschal could be cool.

If they don't receive the special abilities and they have to give up a higher rank for rank 1 in the alternate career what are they gaining other than a select few skills/talents they could elite advance rather than having to elite advance any skills/talents they lost access to by doing so.

Can they for example qualify for those alternate career ranks listed in Into the Storm?

I think if you really want to allow a multi-classing element you have to give them their specials.

I agree with you on things like psykers and navigators they should only be allowed as base classes.

Plus, I like the versertility it would open up. Allowing someone to pickup something like one level of void master and get mastery of small craft or w/e and trade voidfarer. They maybe a seneschal but they are also a hotshot pilot and know a thing or two about a running ships though they're not from a naval background.

You are right, giving the specials would make it a really good option instead of just a "RP"/verstatility-option. For the moment the only player that have done this is the arch-militant + missionary example. She wanted Pure Faith and wanted to spread the word of the Emperor, as she is convinced her life was saved by a miracle.

And qualifying for alternate careers from Into the Storm? Absolutely.

Arch-Militant going Void-Master with specialities Heavy Weapons and Starship Gunnery. "Dakka dakka dakka, that's what I do".

Navigator + Scion + Seneschal seems interesting.

Could be useful for versatility but if you have players prone to power gamers I'm sure some pretty powerful combinations could be made with this system.

One form of multiclassing I considered for a potential Ascension campaign was three ranks in a Rogue Trader class (special ability and all) and then take a transition package to progress into a Dark Heresy ascended class. One player suggested a slight voidmaster variant (master of ground vehicles) progressing into storm trooper for an expert driver.

*shrug* in a game where Powerfists and Storm Bolters exist, not to mention the insane starcraft weaponry, xenos and psykers, powergamers would be made into butter anyway

You'd need rules: (MC = Multi-Class)

Cannot MC into Explorator (Only out of. i.e. if you're an Explorator, you can MC into an Arch-Militant. However an Arch-Militant couldn't MC into an Explorator)
Cannot MC into Astropath ( See Explorator )
Cannot MC into Navigator ( See Explorator )

Yes and no.

IF you are mutant and got Psy rating, you could potentially take the astropath career, but as an unsanctioned and rogue psyker.

Otherwise I agree. Navigator and Explorator are pretty weird.

WhiteLycan said:

With complications like this, wouldn't it be easier to just use elite advances ?

The class-specific traits can also be provided as elite advances.

So what is wrong with using elite advances on a case by case basis ?

Constantly asking a GM to verify entire ranks worth of elite advances can get old very fast and eats into time which could be spent gaming. Better if a mutually agreed solution is worked out beforehand.

I agree with Decessor. There's not much complications really.

Svarte Hanske said:

Navigators are born into Navigator-dom, they cannot be made. Impossible.

Explorators (Tech-Priests of the AdMech) are created through years and years of dedication and selection. Not something you just say "Sure, I'll MC into that"

Astropaths are soul-bound to the emperor. They are blinded permanently but given the gift of seeing out to 30ft through their powerful psychic abilities. This is after the Inquisition rounds them up, trains them for years and years, then brings them to Holy Terra. You don't just say "Hey, I'm a mutant, I'll just go soul-bind myself to the Emperor real quick and gain astral telepathy".

Decessor said:

Which is why you want to empower PCs with that decision making power. As a GM, if a player comes to me with a concept, a proposal for XP they want to spend, and a rationale for the advance, I say do it.

But yes - gettingf as much of this out of the way before the game = essential!

WhiteLycan said:

Unsanctioned = rogue mutant with psy rating that haven't been on Terra and all that. You are right, getting the Astropath special wouldn't really fit, but allowing them to use the scheme to advance could work.