1. Clone wallet sources

git clone https://github.com/Steve-sy/mmrcoinwallet.git

2. Modify CryptoNoteWallet.cmake

set(CN_PROJECT_NAME "mmrcoin-o")
set(CN_CURRENCY_DISPLAY_NAME "MMRcoin")
set(CN_CURRENCY_TICKER "MMR")

3. Set Alternative way is to create git submodule:

git submodule add https://github.com/Steve-sy/mmrcoin-o.git cryptonote

Replace URL with git remote repository of your coin.

4. Build

mkdir build && cd build && cmake .. && make