The configuration of the lifetime of first party cookies is embedded in your JavaScript file regardless of the version of your tag.
For SmartTag
You can change it within the application Tag Composer. Choose your site, choose your configuration and then edit the settings of the "Client-side user ID" plug-in. Finally modify the value of the parameter "Visitor ID Lifetime" (expressed in days).
If you use a third party cookie, then the lifetime of the third party cookie will be 13 fixed months in order to comply with French (CNIL) and European laws. This duration is not configurable.
For Piano-analytics.js
You can change it by setting a new value for the configuration key storageLifetimeVisitor: Javascript | Piano Analytics Developers Documentation (atinternet-solutions.com)