For BTE look at scn for guide like FI Enhancement Technique - How-To-Guide on the Usage of Business Transaction Events
Else look at BAdI FAGL_ITEMS_CH_DATA. This BAdi as well as its equivalent for old accounting FI_ITEMS_CH_DATA receive the whole internal table and not single records one by one as the BTE, so you may optimize database access and response time.
Regards,
Raymond