I have officially concluded my modding journey on this workshop.
As always: feel free to make any kind of submods for any of my mods.

Which Is located here: Open RPFM-Packfile-open from content-max_emp_fleet_updated.pack
You'll find the Nordland Seahawks verianmeshdefinition files in variantmeshes-variantmeshdefinitions-max_emp_nordland_seahawks.variantmeshdefinition
At this point you'll just need to copy the respective Seahawks values of the head/torso/legs slots and past them in the vanilla emp_state_troops_base_ror.variantmeshdefinition file.
Again: even if you have previous experience with RPFM if this Is your first time messing around with variantmeshdefinitions files you might want to read some guide or talk with someone who already have some experience with them since they can be kinda tricky.
A single spelling mistake or wrong line and you'll see broken/invisible models.
You are welcome!
And good luck!

Alrighty, thanks again! :D

The vanilla variantmeshdefinition files regarding the the Nordland Marines are located here:
Open RPFM-Click Packfile-Open from data-variants.pack
There are two files in total that are tied to the Nordland Marines: emp_state_troops_base_ror.variantmeshdefinition which contains the unit's body and emp_state_troops_halberdiers_ror.variantmeshdefinition which contains the unit's weapons.
Since you just want to change the unit models you'll just need to change values in the first one.
Mainly: everything that Is in the head/torso/legs slots.
Keep in mind that directly modifying a vanilla file Is a permanent change, so you might want extract and backup the untouched emp_state_troops_halberdiers_ror.variantmeshdefinition or make a new mod that just overwrites said file when activated.
To modify said file with the Nordland Seahawks variandmeshdefinition lines you'll need to locate my mod first.

I'm familiar with RPFM, I'm just clueless of which exact tables to edit and how to. Thanks!

You'll need to to either use RPFM or PFM and modify the vanilla Nordland Marines' variantmeshdefinition file and change some of the lines inside with some of the Nordland Seahawks' variantmeshdefinition lines.
Is very easy to mess up stuff if you don't know what you are doing so I suggest to read some modding guides and/or visit Da Modding Den https://discord.com/invite/sW49MnP for further help, they can explain things to you in detail better than I could ever do.

In that case how do I mod it so that Nordland Marines wear the same armour/uniform as your Nordland Seahawks?

Not from me, I generally prefer to make new custom units rather than modify any vanilla units.

No plan to change the vanilla Nordland Marines to fit into them?

Updated.
As you can see now the Seamen have two swords, I changed that because while fixing stuff I noticed that this particular unit has a double weapons animation and double swords codes in his variantmeshdefinitions' weapons slot.
I think that It's safe to assume that back then Maxen originally planned to have the Seamen as a double sword infantry all along but failed to do so because of the variantmeshdefinitions' shenanigans (It can be tricky to deal with especially with double weapons).

Awesome thanks so much man I missed these units a lot!

@Mr.Necrophile You are welcome!

Thanks man!