Upcoming Exchange Online Device Access and Conditional Access changes with Outlook mobile

This script actually works to add ActiveSync device IDs correctly for anyone who went with option #3 in this article and was impacted. 

"Manually add the user’s Outlook for iOS and Android Device ID to the user’s ActiveSyncAllowedDeviceIDs property. To obtain the Device ID, use https://docs.microsoft.com/powershell/module/exchange/get-mobiledevicestatistics?view=exchange-ps. To add the Device ID to the user’s ActiveSyncAllowedDeviceIDs property, see https://docs.microsoft.com/powershell/module/exchange/set-casmailbox?view=exchange-ps. An example script is provided that can be modified to automate this"

$mbxids =@()
$mbxs = Get-CASMailbox -Filter { HasActiveSyncDevicePartnership -eq $true } -ResultSize 10000
foreach($mbx in $mbxs)
{
$mbxids = @()
$IDList = Get-MobileDeviceStatistics -Mailbox $mbx.id
$allowedcomps = Compare $idlist.deviceid $mbx.ActiveSyncAllowedDeviceIDs
$blockedcomps = Compare $idlist.deviceid $mbx.ActiveSyncBlockedDeviceIDs
$addallowedid = $allowedcomps | where {$_.sideindicator -eq '<='}
$addblockedid = $blockedcomps | where {$_.sideindicator -eq '=>'}
$mbxids += $addallowedid.InputObject
$mbxids += $addblockedid.InputObject

}
if ($addallowedid.InputObject -gt 0){
$mbxids | Foreach-Object {
Set-CasMailbox $mbx.Id -ActiveSyncAllowedDeviceIDs @{Add="$_"}
}
}