Add a new dynastic rule (or subrule), entitled: “Limitations on Number of Einherjar”, as follows:

Any Einherjar that has been recruited by a Valkyrie and that has not been removed from that Valkyrie’s section of the “Einherjar” wiki page is deemed to be in that Valkyrie’s Portfolio.
No Valkyrie may have more than five (5) Einherjar in her Portfolio at any time.  No Valkyrie may have more than three (3) Einherjar in her Portfolio that share the same Gender.

Add a new subrule entitled: “Trades”, as follows:

Valkyries may transfer any of their Einherjar to any other Valkyrie by posting a story post that announces the transfers.  Transfers may be made conditional on another transfer being made (for example, Valkyrie “X” may announce “I transfer Einherjar “A” to Valkyrie “Y”, conditioned upon Valkyrie “Y” transferring Einherjar “B” and “C” to me.)  An unconditional transfer is effective when announced; a conditional transfer is effective as soon as the condition is satisfied.

The idea being that one should think carefully about “filling up slots” in the Portfolio, rather than grabbing any Einherjar that becomes available).