Here is how I do it (I took the Minuteman of my 2nd UU modcomp for RFC in my sig):
CIV4UnitInfos.xml
Code:
<UnitInfo>
<Class>UNITCLASS_RIFLEMAN</Class>
<Type>UNIT_AMERICA_MINUTEMAN</Type>
<UniqueNames/>
<Special>NONE</Special>
<Capture>NONE</Capture>
<Combat>UNITCOMBAT_GUN</Combat>
<Domain>DOMAIN_LAND</Domain>
<DefaultUnitAI>UNITAI_CITY_DEFENSE</DefaultUnitAI>
<Invisible>NONE</Invisible>
<SeeInvisible>NONE</SeeInvisible>
<Description>[B]TXT_KEY_UNIT_AMERICA_MINUTEMAN[/B]</Description>
<Civilopedia>[B]TXT_KEY_UNIT_AMERICA_MINUTEMAN_PEDIA[/B]</Civilopedia>
<Strategy>[B]TXT_KEY_UNIT_AMERICA_MINUTEMAN_STRATEGY[/B]</Strategy>
<Advisor>ADVISOR_MILITARY</Advisor>
<bAnimal>0</bAnimal>
<bFood>0</bFood>
[...]
The bolded sections are the ones that matter. It doesn't really matter what the code is, but if you do it like this (it's the same as the standard civ 4 code), it is the most easiest way.
After you gave this sections the "code", you can make a new text files. (What I did is: copy the original text file of BTS (CIV4GameText_Civilopedia_BTS.xml) and renamed it to CIV4GameText_
2ndUU.xml. (The bolded section can be what ever you want. In you case, I would name them CIV4GameText_ExtremeMod.xml or something))
After you have done this, you can delete all existing text files in the file you just created. This is what you should left:
Code:
<?xml version="1.0" encoding="ISO-8859-1"?>
<!-- edited with XMLSPY v2004 rel. 2 U (http://www.xmlspy.com) by lcollins (Firaxis Games) -->
<!-- Sid Meier's Civilization 4 -->
<!-- Copyright Firaxis Games 2005 -->
<!-- -->
<!-- Game Text - New -->
<Civ4GameText xmlns="http://www.firaxis.com">
</Civ4GameText>
Now you can fill in the text files.
Code:
<TEXT>
<Tag>[B]TXT_KEY_UNIT_AMERICA_MINUTEMAN_PEDIA[/B]</Tag>
<English>:):):):):)Minutemen were members of teams of select men from the American colonial militia during the American Revolutionary War. They vowed to be ready for battle against the British within one minute of receiving notice. These teams consisted about a fourth of the entire militia, and generally were the younger and more mobile, serving as part of a network for early response to any threat. [PARAGRAPH:1]The minutemen were 25 years old or younger, and were chosen for their enthusiasm, political reliability, and strength. They were the first armed militia to arrive at or await a battle. Officers, as in the rest of the militia, were elected by popular vote, and each unit drafted a formal written covenant to be signed upon enlistment. The militia typically assembled as an entire unit in each town between two and four times per year for training during peacetime, but as the inevitability of a war became apparent, the militia trained more often. The minute companies trained three to four times per week. It was common for officers to make decisions through consultation and consensus with their men as opposed to giving orders to be followed without question, sometimes even in the midst of battle.</English>
</TEXT>
[...]
<TEXT>
<Tag>[B]TXT_KEY_UNIT_AMERICA_MINUTEMAN[/B]</Tag>
<English>Minuteman</English>
<French>Minuteman</French>
<German>Minuteman</German>
<Italian>Minuteman</Italian>
<Spanish>Minuteman</Spanish>
</TEXT>
Make sure the bolded sections are in the Unitinfos.xml and your text file are the same.
(I hope this is clear enough for you)
(I didn't have a strategy, because the RFC civilopedia doesn't show them, but the work the same as the pedia.)
I could kiss you right on the lips! 
