agniveshya sutra is one of lesser practiced sutra of krishna yajurveda .It belongs to one of four upashAkhA of vAdhUla shakha i.e. agniveshya shAkhA.
The following passage from agniveshya grihya sutra describes the yagnopavitham dharan vidhi.
Those who are well versed with taitarIya samhItA will able to trace the mantras. Most of mantras are from taitarIya shAkhA .The mantra for yagnopavitha dharan is quite different from other sutra ( shAkhA ).
Temple priests of ” adIkElAsha Ksetra ”, an old and reputed
place of pilgrimage, some 70 miles to the south of the
town of Tanjore follows this sutra. Only those
belonging to this Sutra are permitted to enter the garbha-
griha or officiate as priests in that temple. The tradition
being that, at the beginning of kaliyuga Siva appeared at
the place before his devotees and ordained that only agniveshya sutra followers should officiate as priests in this temple
and appointed the fore-fathers of the present priests as
hereditary archakas there. There are about only eleven
families following this Sutra and they are all, in one way
or other, related to each other, as may naturally be expected
in the case of a small group marooned in the midst of aliengroups.
( for sake of preservation of lesser practiced veda shakhas and respectively there rituals I have posted this post. Other sutra followers i.e. Apastamba , boudhAyan ,vAdhula posses there own vidhi. I’m not aware about any variation in actual practise from grihya sutra , by this sutra followers. )