Most "mods" ,like catless TBE, will be fine to use without a tune/engine management. Once youre raising boost leavels, intake (?), injectors....then its time for e.m.
But to get the most out of the enhancements youre making to the car e.m. in necessary.
IMO, always remember the ABC's of exhaust mod's: Always Be Catless! it will also decrease egt's alittle and probably give alittle more that 1 h.p. Besides alittle black on youre rear bumper it a tell tail sign of a moded car so people dont f#%# with you ( or do)