This is no new matter, all modders know of it already and as no one obviously cared for it beside FRoGS* the best solution for you is to become your own unless you want to use that submod 
*feel free to VM me if it's in any other and I update this
Here's a tutorial on how to make a portrait http://www.twcenter.net/forums/showthread.php?t=346170&highlight=portrait
Open data/ui/custom_portraits and create a new folder named Eomer
Put the three .tga-files you have created** for Eomer in the Eomer-folder
**or if you may borrow FRoGS version
Add this to the Rohan section of generals in descr_strat.txt (after making a back up of it) found in data/world/maps/campaign/imperial_campaign
Code:
character Eomer, named character, male, age 16, x 198, y 152, portrait Eomer ;east emnet
traits LoyaltyStarter 1 , GoodCommander 2 , ReligionStarter 1 , Loyal 2 , Energetic 1 , Just 1
ancillaries rohan_second
army
unit rohan bodyguards exp 2 armour 0 weapon_lvl 0
unit militia exp 1 armour 0 weapon_lvl 0
unit rohan scouts exp 1 armour 0 weapon_lvl 0
Change, a bit below, from this
Code:
character_record Morwen, female, age 49, alive, never_a_leader
character_record Elfhild, female, age 32, alive, never_a_leader
character_record Theodwyn, female, age 22, alive, never_a_leader
character_record Gleowyn, female, age 20, alive, never_a_leader
character_record Dernwyn, female, age 18, alive, never_a_leader
character_record Eomer, male, age 6, alive, never_a_leader
character_record Eowyn, female, age 5, alive, never_a_leader
into this [Theodwyn's age, Eomer's line should be completly removed and perhaps you want to change Eowyn's age as well but to something closer Eomer's but under 16]:
Code:
character_record Morwen, female, age 49, alive, never_a_leader
character_record Elfhild, female, age 32, alive, never_a_leader
character_record Theodwyn, female, age 32, alive, never_a_leader
character_record Gleowyn, female, age 20, alive, never_a_leader
character_record Dernwyn, female, age 18, alive, never_a_leader
character_record Eomer, male, age 6, alive, never_a_leader
character_record Eowyn, female, age 5, alive, never_a_leader
Open data/world/maps/base and there delete map.rwm
In new campaigns Eomer will be present
If there's any questions or problems post your questions in the Mod Workshop, the part of the froum for modding matters and where skilled modders are plenty and helpful 
concerning coding: http://www.twcenter.net/forums/forumdisplay.php?f=276
concerning portrait: http://www.twcenter.net/forums/forumdisplay.php?f=274
Best of luck 
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