The code that you are showing a snippet of there, is that being done in QlikView code or SQL code?
When you load from SQL you can issue any transact statement you wish after the SQL prefix, eg:
GETDATE() as Now,
DAY(Date) as Day,
MONTH(Date) as Month,
YEAR(Date) as Year,
SUBSTRING(Description, 1, 3) as Prefix
In this case all of the commands are issued against the SQL database and the syntax is as per that of the database.
The 'preceding load' allows you to do all of the data manipulation you could do to fields in SQL, only using QlikView syntax. The above statement could therefore be written as:
now() as Now,
Day(Date) as Day,
Month(Date) as Month,
Year(Date) as Month,
mid(Description, 1, 3) as Prefix
Now, because when loading from Excel you don't get the separate SQL syntax part of the statement you are limited to only issuing QlikView statements, but you can do these in exactly the same way.
Something you need to be careful of when loading from Excel (or even more so text files) is the format of date fields. If they are coming through as strings rather than actual dates then issuing date functions will fail. In these cases you may need to convert the string to a date before issuing another function on them, eg:
Day(Date#(Date, 'DD-MMM-YYYY')) as Day,
This depends entirely on your source data.
Hopefully that has given some pointers as to what you need to do here.
Please post back with more information if it has not.