Found my answer here. The secret is to define a filter attribute, and filters to it.
Thanks @rpwong!
The edited version of the above now works.
# Event log filters
#
# custom filters for events.log
log4j2.appender.event.filter.lognoise.type = Filters
#
# Supressing the noise from the 5-second updates from the ACP UPS
log4j2.appender.event.filter.lognoise.apcjunk.type = RegexFilter
log4j2.appender.event.filter.lognoise.apcjunk.regex = .*(APC_Raw|APC_DATE|APC_LOADPCT|APC_TIMELEFT|APC_LINEV|APC_BATTV).*
log4j2.appender.event.filter.lognoise.apcjunk.onMatch = DENY
log4j2.appender.event.filter.lognoise.apcjunk.onMisMatch = NEUTRAL
#
# Supressing the noise from Astro sun and moon elevation changes, and NTP Time
log4j2.appender.event.filter.lognoise.astroelevation.type = RegexFilter
log4j2.appender.event.filter.lognoise.astroelevation.regex = .*(CurrentDateTime|Date changed from|Elevation).*
log4j2.appender.event.filter.lognoise.astroelevation.onMatch = DENY
log4j2.appender.event.filter.lognoise.astroelevation.onMisMatch = NEUTRAL
#
# Supressing the noise from presence tracking ... TODO: need to send this to a different log if possible
log4j2.appender.event.filter.lognoise.presence.type = RegexFilter
log4j2.appender.event.filter.lognoise.presence.regex = .*Presence_.*
log4j2.appender.event.filter.lognoise.presence.onMatch = DENY
log4j2.appender.event.filter.lognoise.presence.onMisMatch = NEUTRAL