Whiplash99 wrote:Is there a stat to see how often the CO is folding to a preflop 3bet by BTN?
There is a built-in statistic called 'Fold to PF 3Bet After Raise OOP'. Setting that statistic to the 'CO' position using a filter or under 'Item Properties' in the HUD Profile Editor will give you what you want since only the BTN can 3Bet in position vs the CO.
Whiplash99 wrote:Or for that matter each position vs. a specific position's preflop fold vs a preflop 3bet.
There are built-in 'Fold to PF 3Bet After Raise IP/OOP' stats for in position (IP) and out of position (OOP), but not vs specific positions but they could be built - see this guide
for the basics on custom statistics creation and this guide
for a deeper walkthrough. To specify the position of the 3bettor you would use the aggressors string as described here