Hi Bjorn
try this
$principal = New-SPClaimsPrincipal "contoso\jane" -IdentityType WindowsSamAccountName
$spapp = Get-SPServiceApplication –Name "Contoso Visio Graphics"
$security = Get-SPServiceApplicationSecurity $spapp –Admin
Grant-SPObjectSecurity $security $principal "Full Control"
Set-SPServiceApplicationSecurity $spapp $security –Admin
(Get-SPServiceApplicationSecurity $spapp -Admin).AccessRules
Instead of visio you can provide search services app, for more details check this link
http://technet.microsoft.com/en-us/library/ee704546.aspx
Raghavendra Shanbhag | Blog: www.SharePointColumn.com
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