Do not give other users and groups permissions on this file.
You have two accounts: user1 on cluster1, and user2 on cluster2. To run jobs in either cluster, configure .lsfhosts as shown.
You have the account user1 on cluster1, and want to run jobs on cluster2 under the lsfguest account. Configure .lsfhosts as shown.
You have a uniform account name (user2) on all hosts in cluster2, and a uniform account name (user1) on all hosts in cluster1 except hostX. On hostX, you have the account name user99.
To use both clusters transparently, configure .lsfhosts in your home directories on different hosts as shown.