Changing textures and backgrounds in .lua

[Toecheese]

Hi all
forgive me if this is a dumb question but I'm new to lua and and completely stuck!

I understand that nUI textures can be changed in skins using:

nUI_TopBars1:SetTexture("Interface\\AddOns\\nUI_TESTSKIN\\nUI_TESTSKIN_01" );

I understand that this changes the textures called in the .xml file, but how can I change the bgFile and edgeFile to change the background and edges of various frames.

Theres two things stopping me here, first is I simply don't know what the .lua would be!
Could it be something like:

nUI_UNITFRAME_SOLOPLAYER: bgFile ("Interface\\AddOns\\nUI_TESTSKIN\\nUI_TESTSKINbg.blp" ) ;

Secondly, unlike the top bar, bottom bar and dashboard which have their texture applied in the .xml, the untiframe borders and backgrounds are applied in each of the relevant .lua files which by my count is 82 different files!!
(every file in nUI\Layouts\Default\UnitPanels)

Is it possible to add lines in the .lua of a skin to also change all these borders and backgrounds together, or would each file need manually changing?

Thanks a lot
TC