Hi Chris,
Thank you for your interest in Syncfusion Products.
Currently EssentialDocIO do not have support for preserving table styles,so the template containing tablestyles connot be preserved after performing the mailmerge.As a workaround we can use the mailmerge event handler to apply the color for the alternative rows during runtime.We have prepared the sample for your requirement.Could you please find the sample from the below link and let us know if this help.
Sample link:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=F93124724956797.zipPlease let us know if you have any queries.
Regards,
Poornima