Replacements in custom build script

src/freedombone-image-make

 echo $'Changing values within customised customisation script'
 cp "$PROJECT_INSTALL_DIR/${PROJECT_NAME}-image-customise" "$TEMP_CUSTOMISE3"
 if [ "$MYUSERNAME" ]; then
-    sed -i "s|MY_USERNAME=.*|MY_USERNAME=${MYUSERNAME}|g" "$TEMP_CUSTOMISE3"
+    sed -i "0,/MY_USERNAME=.*/s//MY_USERNAME=${MYUSERNAME}/" "$TEMP_CUSTOMISE3"
 fi
 if [ "$MYPASSWORD" ]; then
     sed -i "s|MY_PASSWORD=.*|MY_PASSWORD=${MYPASSWORD}|g" "$TEMP_CUSTOMISE3"
 sed -i "s|SSH_PUBKEY=.*|SSH_PUBKEY=${SSH_PUBKEY}|g" "$TEMP_CUSTOMISE3"
 sed -i "s|GENERIC_IMAGE=.*|GENERIC_IMAGE=${GENERIC_IMAGE}|g" "$TEMP_CUSTOMISE3"
 sed -i "s|MINIMAL_INSTALL=.*|MINIMAL_INSTALL=\"${MINIMAL_INSTALL}\"|g" "$TEMP_CUSTOMISE3"
-sed -i "s|SSH_PORT=.*|SSH_PORT=\"${SSH_PORT}\"|g" "$TEMP_CUSTOMISE3"
+sed -i "0,/SSH_PORT=.*/s//SSH_PORT=\"${SSH_PORT}\"/" "$TEMP_CUSTOMISE3"
 sed -i "s|ONION_ONLY=.*|ONION_ONLY=\"${ONION_ONLY}\"|g" "$TEMP_CUSTOMISE3"
 sed -i "s|PROJECT_REPO=.*|PROJECT_REPO=\"${PROJECT_REPO}\"|g" "$TEMP_CUSTOMISE3"
 sed -i "s|DEBIAN_INSTALL_ONLY=.*|DEBIAN_INSTALL_ONLY=\"${DEBIAN_INSTALL_ONLY}\"|g" "$TEMP_CUSTOMISE3"