What I was wondering after reading that 0 sats/vByte transactions can at least make it to the mempool, if you could simply send an infinite amount of transactions to clog up up the mempool? This transactions will never spam the blockchain, but wouldn't clogging up the mempool be enough to mess with the network. Imagine somebody does millions of transactions per day and will not stop because for him it is essentially free.
By adjusting your node's configuration, yes, you can accept 0-fee transactions to your own mempool.
However, when relaying that transaction to your peers, you'll see that almost all of them wont accept it.
In that scenario, only those nodes that accept 0-fee transactions will be affected by the spammer.
IMO, the damage isn't even serious because a node's mempool has a default size limit so, it won't accept any more 0-fee transactions if the limit has passed and will drop a number for any 1+ sat/vB transaction received.