Ability to add investment cost/date for transferred investments

I am considering transferring my existing S&S ISA to Freetrade in a few months time.

I assume after I transfer my funds into Freetrade my investment/portfolio performance will be calculated relative to the value of the investments at the point they were transferred to the Freetrade platform. Can anyone confirm?

What I would really like is for the performance to be calculated relative to when I started investing several years ago not from when the investments were moved to Freetrade. Therefore, for transferred investments I would like to be able to manually specificy the original purchase price/date so that the Freetrade portfolio tracker can use this information.