Something

#!/bin/bash

cat muhrc |grep -v "nickname =" > muhrc

echo -e "
nickname = \"$1\"\;\n
altnickname = \"$1|1\"\;\n
altnickname2 = \"$1|2\"\;\n
altnickname3 = \"$1|3\"\;\n
altnickname4 = \"$1|4\"\;
" >> muhrc