you will need a few files for that:
- StrategicDecks (at yourmod\GameData\Generated\Gameplay\Decks)
- Units (at yourmod\GameData\Generated\Gameplay\Unit\Strategic) and
- MODDING (excel file at yourmod\GameData\Localisation)

Now, you find the battalion whose name you want to change in StrategicDecks
(lets use this as an example, what you are looking for is bolded:

export Descriptor_Deck_GR_KG_Altrock_solo_Pion_GR_2SR_T is TDeckDescriptor
(
DeckDivision = ~/Descriptor_Deck_Division_GR_KG_Altrock_solo
DeckIdentifier = 'Pion_GR_2SR_T'
Superior = ~/Descriptor_Unit_Pion_GR_vAltro
DeckPackList =
[
TDeckPackDescription
(
Quantity = 1
DeckPack = ~/Descriptor_Deck_Pack_Pion_GR_2SR_T_1__Marschkompanie
ExperienceLevel = 0
),
TDeckPackDescription
(
Quantity = 1
DeckPack = ~/Descriptor_Deck_Pack_Pion_GR_2SR_T_2__Marschkompanie
ExperienceLevel = 0
.
.
. and it goes on, not important part, look up for "DeckIdentifier")
)
---------------------------------------------------------------------------------------------------------
now copy the name in quotes (here it is Pion_GR_2SR_T) and go to Units
There use ctrl+f and find the

export Descriptor_Unit_Pion_GR_2SR_T is TEntityDescriptor
(
DescriptorId = GUID:{51d9757f-1089-4041-9cee-3013fce85d24}
ClassNameForDebug = 'Pawn_Pion_GR_2SR_T'
Modules = [

.
.
. and it goes on, now you are looking for the //PawnUI values
it looks like this, you can scroll down or use ctrl+f again
---------------------------------------------------------------------------------------------------------

// PawnUI
TPawnUIModuleDescriptor
(
HintToken = 'MBT'
NameToken = TBUCKToolAlternativeValues_TLocalisationStringTokenFromTEugBMutableBoolean
(
CommandNameTrigger = ~/SpecificCommandName/UpdateGUIFromStrategicPawnName
Alterator = $/GUIOption/StrategicPawnName
Values =
[
(~/LocalisationConstantes/dico_unites, "VWFCWUDTSC"),
(~/LocalisationConstantes/dico_unites, "GR_2SR_T"),
]
)
ProdMenuTexture = 'Texture_Button_Pawn_Pion_GR_2SR_T'
CountryTexture = 'CommonTexture_MotherCountryFlag_HON'
),
---------------------------------------------------------------------------------------------------------

you need LocalisationConstantes and what is in the quotes, in this example GR_2SR_T
you copy and go to the MODDING and paste it in the first column (TOKEN column) and under REFTEXT you write your new name for the battalion.

Save the file and generate the mod.
---------------------------------------------------------------------------------------------------------

Word of warning, some tokens are reused for multiple batalions, units companies and so on so sometimes it better to put a new token and replace theirs. In this example it would just mean that you change GR_2SR_T to anything you like (for example GR_2SR_TM) in Units and you paste the new token (GR_2SR_TM) into MODDING file under TOKEN column and again add your own text under REFTEXT.

Hope this helps, if its unclear or confusingly written just say