Insert text in every Nth cell

Here is the sample Spreadsheet: https://docs.google.com/spreadsheets/d/1wlO33EWcERa0yYL2xb3BINFt5f441p9MbcB2mPe8eZQ/edit?usp=sharing

I need to insert the text in cell D1 into every third cell in Column C.
You can see in Column E what I am trying to do, and I don't want to have to do it by hand.
Essentially, I need to put %C123H before each paired 88# and T#.
The 88 is an ID and the T# is a device linked to the 88 number. I can then upload the entire list as .txt file into our school inventory system.