You can't cheat for membership. It does not work and it is against the rules for Moshi Monster members.
However, there is a Basic Membership for Moshi Monsters which is free, but you will not be able to do all the activities or catch all the Moshlings. With a Basic Membership, you can get all of the moshlings except the ones that need a Snap Apple, a Crazy Daisy, or that are part of a Super Moshi Mission, or that need a Limited Edition Code for a specific seed. You can keep 2 moshlings in your house and keep one moshling in your backyard.
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You can not get more rooms on Moshi Monsters unless you become a paid Moshi Monsters member.
You have to be either a free Basic Member or a paid Moshi Member on Moshi Monsters to get moshlings.
Cheating is not allowed on Moshi Monsters.
Cheating/hacking is not allowed on Moshi Monsters. You will lose your Moshi Monsters account if you cheat or hack.
You would have to open 100 different Moshi Monsters member accounts to have 100 different Moshi Monsters.