bitcoin core – Can a unconfirmed transaction be lost or modified?

I am beginner and I am still learning fundamentals of block and bitcoin network.

Suppose, I do a transaction on bitcoin network, it is marked as unconfirmed transaction and is stored in mempool of full nodes.

This unconfirmed distributed over network, at some point a minor will create a block which will contain this transaction.

My question is where these unconfirmed transactions are stored before being included in block or hence block chain?

Can they be modified before a minor put them in blockchain?