Using a DATA step approach for "importing Excel" data, you have complete control of the SAS INFORMATs that are used with the INPUT processing logic.
I don't use PROC IMPORT and so I don't know of a way to override SAS PROC IMPORT and its GUESSINGROWS determination by supplying your own INFORMAT statement that gets generated by SAS during the PROC IMPORT process?
Although, depending on the data-format, it may be possible to use a SAS variable that has been "input" and then use a PUT function to assign your own variable, rather than looking for a "hook" to override SAS.
Suggest the OP explain in more detail what input and output should appear like, and ideally, if available, contribute actual SAS-generated log as a post/reply to the forum detailing the challenge. You're better off providing specific instance condition rather than just asking an open-ended question as has been done with this post.
Scott Barry
SBBWorks, Inc.