You can set the template in doku.php:
$conf['template'] = '<template>';
You can check the $INFO array to get the current user: $INFO['client']. And there you also can check to see who is an admin. If by process and instructions descriptions you mean wiki pages that have certain data in them, then you can check the page $ID. So:
if($ID == "doc:process') {
$conf['template'] = 'proces';
}
ETC.
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Edit:
Sorry. Missed the "not for the look of the wiki" part of your request. The above would of course do that, change the main DW template.