Unfortunately, Electrum focuses only on Bitcoin storage for the purpose of both convenience and security not for the altcoins that you have said above.
So, it means the official Electrum wallet is for Bitcoin only. You can't modify the source code because of security reasons.
However, there's an Electrum wallet for these altcoins.
- For LTC --> electrum-ltc.org
- For BCH --> electroncash.org
- For DASH --> electrum.dash.org
All of them are cloned with Electrum wallet by its own features. If you want to use a multi-sig wallet just use an alternative to Electrum.