The simple answer is that you will not be able to play LOTRO with the Mac client unless you have Admin account or at least access to one on the computer you use. This is because Admin rights are required to check file/ folder permissions and change them which are required for any changes to the client.
Originally Posted by Brulac
There is no way around this. You will need to gain access again to the Admin account each time it is updated or the client decides it needs to change anything.
Gaspard Strongpole - Hunter on Eldar : Mac Player - iMac/27-inch, Late 2013/ 3.4 GHz Intel Core i5/ 8 GB 1600 MHz DDR3/ NVIDIA GeForce GTX 780M 4096 MB/OS X 10.10.5