In On-prem environment the icon of a published application can be replaced through the Application properties GUI. However in Citrix Cloud customized icon replacement is not possible from the GUI. We can use Remote PowerShell SDK to get it changed

Instructions

With Citrix Cloud, application icons are either the defined “application.exe” ico or a set of pre-set icon like below.

Note-It's suggested to use the following sizes initially, 128 X 128 or 256 X 256.

To have the ICON replaced with a different / customized icon follow the below steps:

1) Download the remote PowerShell SDK for Citrix - https://download.apps.cloud.com/CitrixPoshSdk.exe 
2) Install the PowerShell SDK with Admin rights
3) Launch the PowerShell SDK in elevated mode
4) Run the following commands
    ASNP Citrix*
    GET-XDAuthentication
5) Enter the credentials when prompted for the same

6) Save the customized icon in the C:\ drive
7) Run the following command

$icon=Get-BrokerIcon -FileName "<Location of the .ico file>" |New-BrokerIcon | Select-Object Uid
Get-BrokerApplication -name "<Name of the published application>" | Set-BrokerApplication -IconUid $icon.Uid

Message will be displayed only if fails. If no message is displayed it confirms success. Refresh the StoreFront web page and check the icon, it should be changed.

Note: If you are having issues running the command "Get-BrokerApplication -name "<Name of the published application>" | Set-BrokerApplication -IconUid $icon.Uid" and receive an error response informing "Object does not exist", please confirm you are using the applications name in the command and not the published name. 
 
To check this, simply run the "Get-BrokerApplication ", search for the application which you want to edit the icon for, and check that you are using the name which is provided in the "Name" Parameter and not the "PublishedName" Parameter.