You would have to look in the original file that the POIs came in. If there is an icon specified, you can change it in that file. If you want them all to be the same, you can just do a search-and-replace with your editor.
If there is no icon specified in the original file you need to find out the file format to see where the icon information would go. Then you could paste the icon info into each record in the original file. That's still a bit tedious but it would be quicker than doing it in Mobile PC.
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