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Oh dear, disappointing that you have not yet had any replies. I haven't really got into modding for TS4 myself so I can't help, but if you don't get any luck here you could try at
http://sims4studio.com/ where they offer a modding tool that does the task you want to do and also are active in offering support and tutorials for it.
"You can do refraction by raymarching through the depth buffer" (c. Reddeyfish 2017)