This peaked my curiosity, so I took a quick look.
Only flavors from the <Flavors> table that look like they might apply are
FLAVOR_ESPIONAGE
FLAVOR_DIPLOMACY
I took a look at Alexander, since he's in all three expansions.
Vanilla
Code:
<Row>
<LeaderType>LEADER_ALEXANDER</LeaderType>
<FlavorType>FLAVOR_DIPLOMACY</FlavorType>
<Flavor>9</Flavor>
</Row>
G and K
Code:
<Row>
<LeaderType>LEADER_ALEXANDER</LeaderType>
<FlavorType>FLAVOR_DIPLOMACY</FlavorType>
<Flavor>9</Flavor>
</Row>
<Row>
<LeaderType>LEADER_ALEXANDER</LeaderType>
<FlavorType>FLAVOR_ESPIONAGE</FlavorType>
<Flavor>5</Flavor>
</Row>
BNW doesn't change either of these two flavors.
To give a compare, Washington has a FLAVOR_DIPLOMACY=7 in Vanilla
In G & K Washington has FLAVOR_DIPLOMACY=7 plus FLAVOR_ESPIONAGE=7
In BNW no change to these two flavors from G & K.
My guess (and it is only a guess based upon the Flavor seems to stay the same between expansions for the same leader) would be that FLAVOR_DIPLOMACY is not related to choice between Diplomats or Spies but rather trend to talk-talk instead of fight-fight.
No guess on FLAVOR_ESPIONAGE and whether higher number means more likely to steal techs via spies, or more likely to establish Diplomats.
To get a better idea it would be needed to look at all leaders for these two flavor settings. Also perhaps the answer is really in the DLL or LUA.