All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all His family and companions.
It isn`t permissible to finance decorations for stores through Murabaha since this sale/transaction is about existing commodities which are purchased and received by the merchant, then sold to the customer. However, since decoration works in this case are non-existent commodities, Murabaha sale/transaction isn`t valid. Rather, these decorations take the ruling of non-existent commodities, and financing them is considered a forbidden loan because it involves usury {Riba}.
The alternative is that the customer concludes an Istisnaa` contract (Making on customer`s order) with the financing institution to have the decorations of his store made, because this contract is about the commodities to be manufactured and are non-existent at the time this contract is concluded. And Allah knows best.