Autocomplete taxonomy fields

I'm trying to prepopulate a taxonomy text field which has autocomplete on.

<input type="text" class="form-text form-autocomplete required" value="" size="60" id="edit-field-service-address-value" name="field_service_address[value]" maxlength="255" autocomplete="OFF"/>

I have tried with edit[field_service_address][value] and edit[field_service_address][value][autocomplete] but it won't fill it.

I've read about #360613: Prepopulating CCK Autocomplete Nodereference field, but it doesn't seem to be a similar problem.

I'm just asking if prepopulate can be used to fill these kind of fields? I noticed that to fill the values with PHP in custom module I need to do it in #pre_render function, because CCK hasn't build the whole form yet when using form_alter function (for example CCK fields are not inside any groups when using form_alter).