The BoR and the entire issue of what constitutes "unmodified leadership" have been severely confused by conflicting FAQs, the most recent of which are as follows from the general, skaven & lizzie FAQs, respectively:
Q: When taking a Leadership test, sometimes you have to take it on your unmodified Leadership. What is your unmodified Leadership? (p10)
A: Your unmodified Leadership is the highest Leadership characteristic in the unit. So the Leadership from any characters in the unit itself (but not from outside the unit, from Inspiring Presence for example) with a higher Leadership can be used unless specifically stated otherwise.
Page 33 – Strength in Numbers. Change the second sentence of the first paragraph to “Units
with the Strength in Numbers special rule add their current rank bonus to their Leadership value for any Leadership test.”
Q: If the Blade of Realities hits a target with no Leadership value, such as a Screaming Bell, does it automatically fail the test, and is therefore instantly destroyed? (p99)
A: Yes.
IIRC, the skaven and general FAQ answers have changed at least three times each so having an older FAQ versus the most current FAQ can cause even further confusion. For the BoR specifically, it appears fairly conclusive (for the moment) that the LD value used is the one on the model's profile and not it's "unmodified LD" since hitting the bell clearly ignores the highest LD characteristic in the unit. The FAQ for the lore of death spell, Spirit Leech, further clouds the issue of unmodified LD since it ignores the spell's wording and allows inspiring presence to be used.
All of this to say that while I believe the BoR uses the LD characteristic of the model it is striking, one is likely to encounter dissenting opinions due to the contradictory FAQs. As Rycheck has indicated, the BSB re-roll is allowed since it is simply a re-roll and not an adjustment to LD.