If the strings of a Tzitzis tore and became invalid, may one unravel some of the loops in order to validate its length?
No.<a href="#_ftn1" name="_ftnref1">[1]</a> However some Poskim<a href="#_ftn2" name="_ftnref2">[2]</a> rule that in a time of need that other Tzitzis is not available, one may do so.
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<a href="#_ftnref1" name="_ftn1">[1]</a> P”M 12; Rav Akiva Eiger; See Biur Halacha 12 “Yeish Lismoch”; Tehila Ledavid 12:5
<a href="#_ftnref2" name="_ftn2">[2]</a> Beir Heiytiv 12:6 in name of Halachos Ketanos 2:112

Shulchan Aruch HaRav | If the strings of a Tzitzis tore and became invalid, may one unravel some of the loops in order to validate its length?

If the strings of a Tzitzis tore and became invalid, may one unravel some of the loops in order to validate its length? No.[1] However some Poskim[2] rule that in a time of need that other Tzitzis is not available, one may do so. _____________________________ [1] P”M 12; Rav Akiva