Do you need a custom extension in order to make/remove range blocks on IP's like they do on Wikimedia?
What about a range calculator? Is this available as an extension? Also, what about the abusefilter rangeblock feature? The corresponding system messages exist, but the actual feature doesn't.
You need to use a rangeblock calculator on the web.
And with AbuseFilter, it's disabled by default though I've never seen it used and I'm not sure if it works/how it works.
Rangeblock is not enabled by default on abuse filters. The default functions are array( 'flag', 'throttle', 'warn', 'disallow', 'blockautopromote', 'block', 'degroup', 'tag' ). Also, https://tools.wmflabs.org/blockcalc/ is usually operational. Usually.
@Void which spot in which GitHub file did that array come from? I would like to be able to replace degroup with rangeblock, as the abuse filter "user account" does not have the technical ability to degroup on my wiki (only founder and steward can edit user rights)
The functions are defined by the variable $wgAbuseFilterAvailableActions. This variable is not defined in the mw-config repository, but is set to the above defaults according to the documentation of the extension.
@Void so if it's not currently defined, how do I customize it? Where could it be defined, without breaking syntax?
Likely in your block of LocalWiki.php set
$wgAbuseFilterAvailableActions = array( 'flag', 'throttle', 'warn', 'disallow', 'blockautopromote', 'block', 'degroup', 'tag', 'rangeblock' );
LocalWiki.php should be used for overrides only. The config should be in this section.