so the Rondelero Swashbuckler has the following ability.
Falcata Emphasis (Ex): At 1st level, a rondelero swashbuckler is proficient with falcatasUE and can treat a falcata as a one-handed piercing melee weapon for the purposes of the swashbuckler’s finesse as well as all feats and class abilities that refer to such a weapon. This ability replaces the derring-do deed.
would this allow him to use a large size falcata in 2 hands and treat it as a 1handed piercing weapon?
If you're wielding a large falcata you're most likely str based
I see nothing preventing you from using the following deeds while wielding two handed
As a swift action, a swashbuckler can spend 1 panache point to double her precise strike’s damage bonus on the next attack. This benefit must be used before the end of her turn, or it is lost. This deed’s cost cannot be reduced by any ability or effect that reduces the amount of panache points a deed costs (such as the Signature Deed feat).
In fact a str based should be better at riposting as they are most likely to be enlarged and not take size penalties to the riposte vs larger enemies