I want to modify the value of count in JSON Input like that

but it dosn't work,however,it work for other Metric Aggregation,sum, min and so on.

You cannot add an inline script in the JSON input, but you could achieve a similar result by using a Scripted field in Kibana, where you set it's value as "100" and then do a Sum metric on that field instead of the Count.
Thank you for your answer very much,I'll try it.