First, go through the addon and remove every SetShadowOffset call.
Then, find every place the addon calls code like this:
Code:
local fontString = frameObject:CreateFontString(...)
Immediately after each CreateFontString call, add a new line:
Code:
fontString:SetShadowOffset(0, 0)
Also check for any code like this:
Code:
fontString:SetFontObject(...)
If such a line appears right after the CreateFontString call, then move your SetShadowOffset line after the SetFontObject line. If it appears somewhere else (such as in an options function) add another SetShadowOffset line right after it.