You will need to go to the pyfolio files and make certain changes. At this point I am not sure whether I should go to pyfolio github repository and do a pull request because my changes work for what I need in the context of backtrader. I am in no way certain that making these changes will not break something else in pyfolio.
In round_trips.py, I made the following changes
Essentially, you now cannot pass rename logic in the dicts themselves. This also means that for you will need to create a list of the column names and pass it yourself.
this is the updated code Main changes are that we are creating a list of column names col_list before each function call to pass to the agg_all_long_short function (for reasons explained above - pandas deprecating nested renaming)
Based on one old comment from the 'bt' author (search forum for 'lineplotterindicator') 'lineplotterindicator' was made to quickly show a line. So you may need to make an indicator from 'self.inds['signal1']' to be able to customize it's plotting.