Es its a bit try.
You probably need to either send the object-parameters as one long
string.
The php needs to store this info (Sql or textfile) as a
specific entry.

When doenloading you need to send a list of entries.
The player selects one, and the php then sends back this
string with object entries.

To make it work offline, you need to save these new files
then locally.

A bunch of work for you

Or you go with saving new level locally into files firt.
Make a little forum to upload the new levelpacks.