Hi, my name is Matt S Rinc and as video screencasting pro from 2007 I can help you.
I understand you need to mix intro and outro to your videos (or provide more details) plus change a parameter or add caption first 5-10 seconds etc. Please let me know.
At a rate of 75 videos per day (8-10 per hour for simple, repeated changes to all movies) it can be done in 14 days.
Do note that source, uncompressed videos are preferred. MPEG 4 compressed videos will (although small but will) loose additional visual quality no matter if you use highest quality output parameters.
Best Regards,
Matt