Another function of tone change is noun specialization and/or semantic shift.

For an example of specialization, we can take a look at the word 城 [siaŋ22] city/town. A change in tone to 225 would mean specifically the town of Taicheng (台城), the county seat and largest town in Taishan. To residents of the town, it would be just the couple of blocks where the town originated.

By the way, 城 is widely used to name county seats in the Pearl River Delta area, i.e. 会城 is the county seat of 新会 (Xinhui), and 莞城  of 东莞 (Dongguan, now a pop. 5 million+ city sandwiched between Guangzhou and Shenzhen). 广州 (Guangzhou/Canton) is also known as 省城 [saŋ55 siaŋ22]-- the provincial city.

鼻 [bi32] is nose, but a change in tone to 鼻 [bi325] would be nasal mucus -- a case of semantic shift.

Here are some more examples:

	Normal Tone	Changed Tone	Normal Tone	Changed Tone
烟 [yan]	33	335	smoke	tobacco
糖 [hɔŋ]	22	225	sugar	candies
头 [həu]	22	225	head	leader
妹 [mɔi]	55	21	young girl	younger sister
月 [ŋut]	32	215	month	the moon
公 [gǝŋ]	33	215	old person	(of animal/insect) a male; (of chess) the King
墨 [mak]	32	215	ink	a mole
山 [san]	33	21	mountain, hill	a burial heap
尺 [tsiak]	33	21	measurement unit of one foot	a ruler
二 [ŋi]	32	215	the number two	(intimate) the second son; (playing cards) a card of rank two
拳 [kun]	22	225	fist	a set or style of Martial Arts
脚 [giak]	33	21	feet, leg	dregs
银 [ŋan]	22	225	silver	money
日头 [ŋit hǝu]	33-21	21-215	the sun	day time
鸡笼 [gai lǝŋ]	33-21	33-215	chicken cage	a type of fried dumpling (shaped like a chicken cage)
火头 [fɔ həu]	55-22	55-225	source of fire; seeds of trouble	a cook