[Baertram]

Transmute crystals are not saved per each toon but account wide.
So it does not matter who opens any geode as long as you are not near the 1000 max.

Edit:
Sorry, I didn't see this was asked in the addon search, thought it was addon code/API related:

API functions exist to get the currency types of your logged in char but non that would be able to check other chars (not logged in). You'd have to login with them once and save their crystals to the SavedVariables before being able to know and compare.

h5. CurrencyLocation
* CURRENCY_LOCATION_ACCOUNT
* CURRENCY_LOCATION_BANK
* CURRENCY_LOCATION_CHARACTER
* CURRENCY_LOCATION_GUILD_BANK


h5. CurrencyType
* CURT_ALLIANCE_POINTS
* CURT_CHAOTIC_CREATIA
* CURT_CROWNS
* CURT_CROWN_GEMS
* CURT_EVENT_TICKETS
* CURT_MONEY
* CURT_NONE
* CURT_STYLE_STONES
* CURT_TELVAR_STONES
* CURT_UNDAUNTED_KEYS
* CURT_WRIT_VOUCHERS

* GetCurrencyAmount(*[CurrencyType|#CurrencyType]* _currencyType_, *[CurrencyLocation|#CurrencyLocation]* _currencyLocation_)
** _Returns:_ *integer* _amount_

* GetMaxPossibleCurrency(*[CurrencyType|#CurrencyType]* _currencyType_, *[CurrencyLocation|#CurrencyLocation]* _currencyLocation_)
** _Returns:_ *integer* _max_