howto replace fieldType string with text lowercase

[Bernd Fehling]

Dear list,

for one field I want to change fieldType from string to something
equal to string, but only lowercase.

currently:
<field name="firstname" type="string" indexed="true" stored="true" 
multiValued="true">
<fieldType name="string" class="solr.StrField" sortMissingLast="true" />

new:
<field name="firstname" type="text_lc" indexed="true" stored="true" 
multiValued="true">
<fieldType name="text_lc" class="solr.TextField" positionIncrementGap="100" 
autoGeneratePhraseQueries="true">
  <analyzer>
    <tokenizer class="solr.StandardTokenizerFactory"/>
    <filter class="solr.LowerCaseFilterFactory"/>
  </analyzer>
</fieldType>

Is this the right replacement for "string"?
Are the attributes for solr.TextField ok?

Regards
Bernd