Smrithis..

Then comes the Smrithis. Smrithis depend on the Vedasaakhas one follows. Smrithi is also termed as Dharmashaastra. These are in fact the codes of conduct applicable to Individuals, respective families, respective communities, respective nations, and can vary according to such units, and at the end of every yuga, the smrithis also get submerged along with the living beings and they are again revealed at the beginning of the next yuga. The main smrithis are by Manu, Yajnavalkya, Shankha, Likhita and Parasara…each have created smrithis for each yuge (Krita, Threta, Dwapara and Kali) , separately.
युगान्तेऽन्तर्हितान् वेदान् सेतिहासान् महर्षयः।
लेभिरे तपसा पूर्वं अनुज्ञाता स्वयम्भुवा॥
कल्पेकल्पे क्षयोल्पत्या ब्रह्मविष्णुमहेश्वराः।
श्रुतिस्मृतिसदाचार निर्णेतारश्च सर्वदा॥
yugaante.antarhitaan vedaan setihaasaan maharSayaH.
lebhire tapasaa puurvaM anuj~naataa swayambhuvaa..
kalpekalpe kSayolpatyaa brahmaviSNumaheshwaraaH.
shrutismR^itisadaachaara nirNetaarashcha sarvadaa..

At the end of each yuga Vedas along with itihaasaas disappear and at the beginning of the next yuga the sages, as directed by Brahma the Swayambhu, do penance and gain the knowledge of the Vedas and Itihaasas all over once again. The triumvirate Brahma, Vishnu and Shiva, survive for the whole of each Kalpa (4.32 billion years—now it is Shwethavaraahakalpa) and they are the ultimate lawgivers and providers of Shruthi, Smrithi and code of conduct during the kalpas.
This would imply that there can be changes in Shruthis and Smrithis according to passing years.