code:

# "Converting" a Distribution Group to a Shared Mailbox
function convertdg.mailbox($groupName) {
  $groupMembers=get-distributiongroupmember $groupName
 echo "Users in this group:  $groupMembers.alias"
	newdg grpTemp
 echo "Saving these users..."
	trans $groupName grpTemp
sleep(3)
  remove-distributiongroup $groupName -Confirm:$False
 echo "Creating the new Mailbox..."
  new-mailbox -name (read-host "Display Name of Shared Mailbox?") -alias $groupName -primarySMTPAddress "$groupName@email.com" -shared
 echo "Creating the new, Security-Enabled Distribution Group..."
  newdg grp$groupName
 echo "Adding $groupMembers to it..."
  trans grpTemp grp$groupName
 echo "Adding Full Access and Send As permissions..."
  Add-MailboxPermission $groupName -user grp$groupName -accessrights fullaccess -inheritancetype all
  Add-RecipientPermission -Identity $groupName -Trustee grp$groupName -AccessRights SendAs -confirm:$false
 echo "Cleaning up..."
	remove-distributiongroup grpTemp -Confirm:$False
}

# "Converting" a distribution group to a security group
function convertdg.security($groupName) {
#  $groupName=read-host ("Distribution Group to change?")
  $groupMembers=get-distributiongroupmember $groupName
 echo "Users in this group:  $groupMembers.alias"
	newdg grpTemp
 echo "Saving these users..."
	trans $groupName grpTemp
 sleep(3)
  remove-distributiongroup $groupName -Confirm:$False
 echo "Rebuilding the group..."
	newdg $groupName
 echo "Restoring the users..."
	trans grpTemp $groupName
 echo "Cleaning up..."
	remove-distributiongroup grpTemp -Confirm:$False
}