Litecoin L-addresses are legacy (non Segwit or non-P2SH) addresses.
Litecoin addresses starting with 3 will start as M (to differenciate from Bitcoin addresses).
The complete Litecoin address will change but they point to the same Litecoin address on the blockchain.
You can convert an address from legacy to the new Segwit.
PS: If you use https://changelly.com, to convert cryptos, It can only sent to the old legacy Litecoin address. You have a small challenge here now.
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