Might be best to just ask in the comments of the layout in question, or PM the author.
In oUF_Taroven, which does use that same glowTex you've mentioned, there's two points where you can change things up.
1: In the locals segment at the beginning of oUF_Taroven.lua. Added a couple comments to help.
Code:
local glowtex = mediapath.."glowTex"
-- Note: mediapath.. is a concatenation, that line actually reads...
-- local glowtex = "Interface\\AddOns\\oUF_Taroven\\media\\glowTex"
2: Down where the glowtex is actually used.
Code:
self.FrameBackdrop = CreateFrame("Frame", nil, self)
self.FrameBackdrop:SetPoint("TOPLEFT", self, "TOPLEFT", -4, 4)
self.FrameBackdrop:SetPoint("BOTTOMRIGHT", self, "BOTTOMRIGHT", 4, -4)
self.FrameBackdrop:SetFrameStrata("BACKGROUND")
self.FrameBackdrop:SetBackdrop {
edgeFile = glowtex, edgeSize = 5,
insets = {left = 3, right = 3, top = 3, bottom = 3}
}
self.FrameBackdrop:SetBackdropColor(0, 0, 0, 0)
self.FrameBackdrop:SetBackdropBorderColor(0, 0, 0)
self.FrameBackdrop:SetAlpha(0.6)
Make sure you adjust the insets and edgeSize once you manage to get the texture changed. For most borders, insets of a quarter the edgeSize work pretty well.
I've bolded the portion where the texture is set for ya.