Ref. No. 41/1030
In the name of Allah the most gracious the most merciful
The answer to your question is as follows:
The number 786 is written in order to save Allah’s name from desecration. So, there is nothing wrong in writing 786 as an alternative of bismillah.
And Allah knows best
Darul Uloom Waqf Deoband
This answer was collected from the official website of Darul Uloom Deoband Waqf. The institution is based in India and the answers are provided in accordance to the Hanafi Fiqh.