It supports Epic’s own Temporal AA (Not TXAA), FXAA, and Supersampling by default. The latter two you’re probably familiar with, for the Temporal AA you can read more about it here: https://de45xmedrsdbp.cloudfront.net/Resources/files/TemporalAA_small-59732822.pdf
If you want to add a custom solution, you can download the source and make changes there, but most normal antialiasing techniques don’t work well with deferred rendering (at least not with the same performance as Temporal AA). It might be difficult to get an existing method like MSAA work on the full scene without tanking the framerate.