SOLR exact search turn off stemming

I am using SOLR 4.10 core, and I have a field called PolicyReference with an IDX_PolicyReference index, and I am trying to set up an exact search on this field

So I execute a query like the following:

IDX_PolicyReference:ABC123

This has been working fine for years.

Now devs are sending PolicyReference values that contain a space: for example

IDX_PolicyReference:AB 123

This does not return the exact search result I am expecting.

From reading other questions on SO regarding this, it sounds like I need to turn off stemming.

I can successfully find the PolicyReference if I put double quotes around the value

IDX_PolicyReference:"AB 123"

But I'm trying to solve this without having to change the app that calls SOLR.

The schema.xml has the following elements in it.

<field name="PolicyReference" type="string" indexed="false" stored="true"/>
<copyField source="PolicyReference" dest="IDX_PolicyReference"/>
<field name="IDX_PolicyReference" type="text_Exact" indexed="true" stored="false" multiValued="true" />

<fieldType name="text_Exact" class="solr.TextField" positionIncrementGap="100" >
    <analyzer type="index">
        <tokenizer class="solr.KeywordTokenizerFactory"/>
        <filter class="solr.LowerCaseFilterFactory"/>
    </analyzer>
    <analyzer type="query">
        <tokenizer class="solr.KeywordTokenizerFactory"/>
        <filter class="solr.LowerCaseFilterFactory"/>
    </analyzer>
</fieldType>

My understanding was that when using KeywordTokenizerFactory, it takes the search term as one keyword. But it seems like space breaks it.

Is there another tokenizerfactory that I can use to achieve what I'm trying? Are there other attributes I can apply to the tokenizer xml element, or a filter that I can add that will turn off the stemming for this field - something that I can change in schema.xml and reindex that will allow my search request to work as is?

Again, I'm trying to avoid changing the app that calls SOLR.