FlyerTalk Evangelist
Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: BA Silver, TK E+, AA PP, Hyatt Globalist, Marriott LT Plat, Hilton Diamond
Posts: 13,026
Travel Packages are category-based, so should work on peak dates as well with no additional charge.
For other certificates that are points-based, you can book those now, but changes in 2019 should be subject to the rules applying then.