Once a company is created you are unable to rename it. 

The reason for this is that companies are shared across the TrackMySubs platform.  

For example:

If you select "Dropbox" as your subscription, and you decide you want to rename it to "My Dropbox", the rename would change the name for all users in TrackMySubs.  Hence why it is restricted.

If you would like a custom name of a subscription, simply create it as a new subscription with your preferred name.