Here below is a data table:

The task is to insert one row after the number 100, and fill in a001, a002, … in turn, like this:

Script:

=spl("=E@b(?1).group@i(~[-1].#1==100).(~|new(string(#,""a000""):_1)).conj()",A1:A9)

Group the data. When the value in column A of the previous row is 100, create a new group.
Loop through each group, insert a record at the end of the group, whose value of the first column is the current group number #, formatted with “a000”.

https://c.scudata.com/article/1651916536524
https://c.scudata.com/article/1658708289505
https://c.scudata.com/article/1658803502132