Write a search to modify the contents and update the samelookup
|inputlookup abc.csv | <content modify search> | outputlookup abc.csv
Your <content modify search> can be something like |eval <fieldname>=if(fieldname=="something","newvalue","oldvalue") etc., to update field such as fieldname values with the new content. Above logic varies based on your requirement, please check eval documentation here (https://docs.splunk.com/Documentation/Splunk/8.0.3/SearchReference/CommonEvalFunctions)
Thanks. My objective over here is that i am having some static content which i am loading into the csv file and then reading it using inputlookup. After updating the content curently i have to replace the file in splunk back again.