have you looked at the Karaoke Templater?
http://aegisub.cellosoft.com/docs/Ka...ter_Tutorial_1
http://aegisub.cellosoft.com/docs/Ka...ter_Tutorial_2
It lets you define an effect template and then Aegisub will apply it to the line timings. It's included in aegisub, no extras to install
also
http://aegisub.cellosoft.com/docs/ASS_Tags has all the ASS tags you'll ever need