We noted that, in some cases, you are not able to change the password on Analysis for Office.
This is a know issue and it is related to the .Net Connector (NCo) 3.0.15. The correction will be part of NCo 3.0.16.
I will keep you updated if the correction will be on the Analysis for Office 1.4.13 but as work-around you can change the password directly on the SAPGUI.
Delivered planned dates that will include NCo 3.0.16:
Analysis Office 1.4 SP14, planned for CW40, 2015
Analysis Office 2.1 SP03, planned for CW48, 2015