I don't know about customer owed but the utilities do it all the time around here and I am sure they are not boring another hole for a warning ribbon. They bored a HV line behind my house that I am betting was over 100kv. The existing on the poles is (2)48kv and 250kv.
George Conductors marked with a rated temperature higher than that of the raceway can be used when the conductors are operated within the raceway temperature rating.
One application of 353.10(6) is the use of 105°C-rated medium voltage cables, Type MV, where the cable ampacity at the 105°C rating is reduced to the cable ampacity at 75°C or 90°C to match the listed operating temperature rating of HDPE (75°C or 90°C). Direct bury power cable systems are designed for long life, use of HDPE conduit to encase and protect the power cable from rock impingement is gaining favor as it allows for quick and easy repairs without excavation of the cable. HDPE conduit and innerduct is used to carry low 600V-transformer to end user) and medium (<69kV-substation to transformer) voltage power lines.