Hi Birjit,
I do not believe it is possible to change the name to add another digit.
Instead, I would suggest using the programming interface, as defined in the programmer's manual, to customize your saved files with the
SAVE:WAVEFORM
command.
If you do not wish to get into the SCPI commands, you could also consider using TekScope Utility to achieve the same functionality through its data logging feature:
https://forum.tek.com/viewtopic.php?t=140451