Cross-Origin Request Blocked - Calling get.json on emoncms.org (free account) from outside?

I am using a free account on Emoncms.org , and I would like to slightly modify how Multigraph works. (e.g. increase height of chart region from 400px, fix the initial time window shown).  

This may not be the correct approach, but I thought of making changes within my own local copy of multigraph.htm and multigraph.0.0.1.js , however, the first hurdle I ran into was:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://emoncms.org/vis/multigraph/get.json?&id=nnnn. This can be fixed by moving the resource to the same domain or enabling CORS.

Does this mean that I cannot customize my charts if I use a emoncms.org free account as my primary data store from my emonTH's?

Thank you!