Restrict <w:instrText> Field in Word OOXML

Question

I want to put important data in "w: fldChar" tag, I tried to put that data in "w:instrText" tag, but this code can be changed by user on run time, I want to restrict this field, is their any solution to that?

below is the code sample:

<w:p>
  <w:r>
     <w:fldChar w:fldCharType="begin" />
  </w:r>
  <w:r>
     <w:instrText xml:space="preserve" >"{variable}"</w:instrText>
  </w:r>
  <w:r>
     <w:fldChar w:fldCharType="separate"/>
  </w:r>
  <w:r>
     <w:fldChar w:fldCharType="end"/>
  </w:r>
</w:p>