Is it possible to split off a neighbor's Comcast cable to provide service to my condo?
The cable company will run ONE or more cable lines to a structure. Numerous things drive this decision, and I do believe there is a code they also must follow. This is just an FYI.

That said:

The only thing that would actually prevent the provider from splitting off to "other rooms on the same structure" is signal loss and signal quality measurements.

So is it possible to run multiple units from "one service line" via a number of splitters/taps? ABSOLUTELY and this is standard practice.

When the signal degrades beyond a serviceable quality and equipment cannot operate properly, or customers are complaining of outages, they may rerun cables (in near total futility) OR a wise technician will reduce the taps, use boosters, run another drop, etc.

So you know, every time you split a signal there is an inherent loss in dB. Drop below an acceptable level, and equipment will not perform optimally.