Blocking Ads best practice (bulk updates to URL Groups?)

Question

We use mostly Apple equipment (MacBook, iPhone, iPad) and on our MacBooks we have Little Snitch which is an application-aware outgoing firewall that kills attempts to reach out to advertising sites, trackers, etc. This doesn't help the phones and tablets though. 
 We could do something through DNS perhaps, but it seems like adding the worst offenders to a URL Group to block would work as well. The only problem is, how would you save, modify, or update a URL Group in bulk (i.e. not one-at-a-time through the GUI)? 
 Or is this not best-practice and we should use a different mechanism (DNS Pi Hole or something similar)? 
 (I'm thinking I could feed my discoveries to Sophos somehow to get them to reclassify some sites to Advertising, but that feels slow, they might not agree with my classification, and some folks might want to actually visit the sites in question because they use their services.) 
 P.S. In the Managed TLS Exclusion List there is " ecure.echosign.com" which I imagine is a copy/paste error and should say "secure", but maybe not.

Prism · Accepted Answer

You can create a custom category by importing a txt file with all domains or using an external URL DB. 
 The problem of using the external URL is, It only works over plain-text HTTP or FTP, and It's limited to 2,000 domains, if the file have more it won't work. 
 The same applies if you import a txt file with all domains, It will also be limited to 2,000 domains. 
 If you don't want to go over all the hassle of having to automate everything from fetching the lists, cutting them to fit 2,000 domains per file and having to use the Firewall API to mass import them, then use something as Pi-Hole or AdGuard. 
 PS; If still want to do this over the Firewall, be careful when importing the domains, depending on how fast the processor of your box currently is you will have around >5 minutes of slowness since apparently everything gets inserted over a DB and the process hangs the CPU for a long time. 
 At last It will look something like this:

Blocking Ads best practice (bulk updates to URL Groups?)

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