That the authorities are only giving the guard flag to relays that are fulfilling some (sometimes) high criteria has the purpose to have some stability in the Tor network. Clients aren't searching for a new entry guard everytime they are reconnecting to the network. They are using it for 4-8 weeks. So guards have to be stable.

A Distributed Denial of Service will only (maximally) reach the goal of mean written/read bytes and Advertised Bandwidth. But there is still the uptime requirement that has to be met. So I don't think that a gentle form of DDoS will help you getting the 'Guard' flag. Even if it does there won't be much benefit for the network and maybe you will lose the flag when you stop DDoS.

There would be more benefit for everyone if you just stay straight and keep your relay as it is. If you want to run a reliable relay or even an exit relay you should consider running it on a VPS in an autonomous system. Anyway: thanks for running a relay! :)

Here's my 2nd answer:

If someone else is trying DoSing you over the Tor network there is a chance that this will be prevented from the guard relay. If not it could be an advantage for other relay operators because the traffic that flows through the network goes up to their score.

If this someone is DoSing you over the normal internet I see no chance for other relays to get the guard flag faster except one thing: that the clients are using other relays for their traffic instead of yours so you are missing it because of unreachability.