Hei!
I just tried to figure out, how the diplomacy settings in the startpos.esf is. So here are some things I found out: You can set the behavior of any country to another one. So I can be in war with england, while it thinks, I'm allied. It's maybe useless, 'cause it will propably just lead to bugs (didn't tested everything).
In
main\startpos.esf\CAMPAIGN_STARTPOS\CAMPAIGN_ENV\CAMPAIGN_MODEL\WORLD\FACTION_ARRAY\FACTION_ARRAY\FACTION
you will find the first value as the ID of the faction. Now you go to another Factions
main\startpos.esf\CAMPAIGN_STARTPOS\CAMPAIGN_ENV\CAMPAIGN_MODEL\WORLD\FACTION_ARRAY\FACTION_ARRAY\FACTION\DIPLOMACY_MANAGER\DIPLOMACY_RELATIONSHIPS_ARRAY\DIPLOMACY_RELATIONSHIPS_ARRAY\DIPLOMACY_RELATIONSHIP
and search for this ID. There you can change the likes/dislikes from this faction to the faction, where you looked up the ID.
In DIPLOMACY_RELATIONSHIP_ATTITUDES_ARRAY you have 23 entries. I decrypted some;

2] Example:
1
30
80
True
0
False
The 2. value, here 30, is the value which is shown under "Military pact" (or something like this ingame .. don't have the english Empire installed)

5] Example:
-1
30
0
True
15
True
Here it is the 5. value, shown as "Common enemy".

6] Example:
1
15
60
True
0
False
The 2. value - "Trade agreement".

8] Example:
-2
-140
-200
True
0
False
The -200, 2. is the value for being in war for this faction.

16] Example:
0
10
0
False
0
False
The 2. is the value for the same or different religion.

17] Example:
0
-15
0
False
0
False
The 5. is the value for the same or different regime.

18] Example:
1
40
0
True
0
False
It's the 2. value for historic conflicts/friendship



As you can see, the values for the diplomatic options aren't set at the start from the db, so you are very flexible, when editing in faction. If anyone founds out, what the things around the important values are for, please post. :-)
btw; Things I didn't find out .. how to set the value, when factions leader are disliked and territorial expansion conflicts.