Could use Assistance Configuring IIS Using PowerShell

I need to reconfigure passwords for many IIS servers, and manual setup would take way too long, so I will be using PowerShell to automate the process.
I already have all the pieces to set up specific user authentication for each of the application pools, but could use PowerShell assistance with:

1) Setting the local IUSR_ password:
By the way, the version of PowerShell is 4.0, so I cannot use the Set-LocalUser cmdlet (which was first introduced in 5.1).

2) Setting the website identity (I already have the application pool identity set up):

3) Setting the field Physical Path Credentials Logon from ClearText to Network:

Thanks.