A brief and incomplete guide to the various categories of icons found in a SaintCoinach UI dump https://github.com/xivapi/SaintCoinach

ffxiv_icon_categories

000000: actions
010000: status effects
020000: items
058000: fashions (small), bardings
059000: mount & minions (small)
060000: weather, map markers, market board, player markers, various icons
061000: event actions, markers, gods, pvp, custom deliveries, playstyles, various icons
062000: jobs, beast tribes, map stuff 
063000: hunts, maps
064000: emotes, mount actions, roleplay actions
065000: currency, ocean fishing
066000: macro icons
067000: fashions (large)
068000: mount & minion (large)
069000: mount footprints
071000: credits
072000: blue mage, field records
076000: stickers, mahjong
078000: feesh
082000: trust, orchestrion, island sanctuary
083000: grand company seal
084000: hunts
085000: paintings, flashbacks
086000: mahjong rules, job gauges
087000: triple triad (large)
088000: triple triad (small)
090000: free company crests
100000: journal
111000: guildleves
112000: instances
113000: wondrous tales
114000: new game+
120000: flashes
130000: facepaint (CharaMakeCustomize)
131000: hairstyles
137000: hrothgar
138000: viera
139000: hrothiera facepaint
150000: tutorials
180000: golden saucer misc
190000: portrait backgrounds
191000: portrait frames
192000: portrait decorations
193000: plate backgrounds
194000: plate patterns
195000: plate backings
196000: plate headers
197000: plate portrait frames
198000: plate frames
199000: plate decorations

rename.bat

rem Run this .bat script in your local icon directory to rename all folders for easy reference

ren "000000" "000000 actions"
ren "010000" "010000 status effects"
ren "020000" "020000 items"
ren "058000" "058000 fashions (small), bardings"
ren "059000" "059000 mount & minions (small)"
ren "060000" "060000 weather, map markers, market board, player markers, various icons"
ren "061000" "061000 event actions, markers, gods, pvp, custom deliveries, playstyles, various icons"
ren "062000" "062000 jobs, beast tribes, map stuff "
ren "063000" "063000 hunts, maps"
ren "064000" "064000 emotes, mount actions, roleplay actions"
ren "065000" "065000 currency, ocean fishing"
ren "066000" "066000 macro icons"
ren "067000" "067000 fashions (large)"
ren "068000" "068000 mount & minion (large)"
ren "069000" "069000 mount footprints"
ren "071000" "071000 credits"
ren "072000" "072000 blue mage, field records"
ren "076000" "076000 stickers, mahjong"
ren "078000" "078000 feesh"
ren "082000" "082000 trust, orchestrion, island sanctuary"
ren "083000" "083000 grand company seal"
ren "084000" "084000 hunts"
ren "085000" "085000 paintings, flashbacks"
ren "086000" "086000 mahjong rules, job gauges"
ren "087000" "087000: triple triad (large)"
ren "088000" "088000: triple triad (small)"
ren "090000" "090000 free company crests"
ren "100000" "100000 journal"
ren "111000" "111000 guildleves"
ren "112000" "112000 instances"
ren "113000" "113000 wondrous tales"
ren "114000" "114000 new game+"
ren "120000" "120000 flashes"
ren "130000" "130000 facepaint (CharaMakeCustomize)"
ren "131000" "131000 hairstyles"
ren "137000" "137000 hrothgar"
ren "138000" "138000 viera"
ren "139000" "139000 hrothiera facepaint"
ren "150000" "150000 tutorials"
ren "180000" "180000 golden saucer misc"
ren "190000" "190000 portrait backgrounds"
ren "191000" "191000 portrait frames"
ren "192000" "192000 portrait decorations"
ren "193000" "193000 plate backgrounds"
ren "194000" "194000 plate patterns"
ren "195000" "195000 plate backings"
ren "196000" "196000 plate headers"
ren "197000" "197000 plate portrait frames"
ren "198000" "198000 plate frames"
ren "199000" "199000 plate decorations"