I accidentally clicked 'No' on the following message box and Kile dosen't ask for this again, can I reset this?

my guess, as I don't run kile

there should be a kilerc file in ~/.kde/share/config/ open it an editor and see if there's a variable that seems appropriate and if so reset it

alternative is to completely reset you Kile rc file and maybe the Kile apps folder ~/.kde/share/apps/kile by renaming/moving/removing them

note: some distro's use ~/.kde4 instead of ~/.kde