Alteryx doesn't seem to overwrite an existing sheet in an excel file, so you will need to output a new file or a new sheet each day it runs.
While I get using the word 'append' here, you are really trying to join the new data onto the previous data, using the Profit Center as the common key. You'll just need to get the new day's data organized into two columns, one named "Profit Center" and one "profit data". You can then use the Dynamic Rename tool (developer tools tab) to rename the data column into whatever format you want (likely using some of the Date Time functions and string replace tools to get your desired format).
This can be joined to your existing data pretty easily, even with the dynamic/changing field name for your data column (since you can just deselect the duplicate "Profit Center" column and leave the "Dynamic or Unknown Fields" option checked within the join tool. If your new data is in the right input to the join tool, it should automatically end up as the last column in the resulting joined data set.
This make sense?
