After the end of an AnimateTransform action, the element snaps back to the original value.
This isn't exactly unexpected as it's in the SMIL documentation:

As with all animation elements, this only manipulates the presentation value, and when the animation completes, the effect is no longer applied

But it is unwanted. I'd like to find a way to persist the changes using XML animations

Here's an example in SVG

<!-- begin snippet: js hide: false --> <!-- language: lang-html -->
<svg width="200" height="200" viewBox="0 0 100 100"
     xmlns="http://www.w3.org/2000/svg" 
     xmlns:xlink="http://www.w3.org/1999/xlink">
  <rect id="outline" stroke="black" fill="white" 
        width="100" height="100" >
    <animateTransform id="one"
                      attributeType="XML"
                      attributeName="transform"
                      type="translate"
                      from="0" to="-7"
                      dur="1s" repeatCount="1" />
  </rect>
</svg>
<!-- end snippet -->

One idea I had was to call a set action with dur="indefinite" that was triggered by the end of the first animation with begin="one.end", but can't quite seem to get the syntax right. I haven't found any documentation that show how to call set for a transformed value.

<!-- begin snippet: js hide: false --> <!-- language: lang-html -->
<svg width="200" height="200" viewBox="0 0 100 100"
     xmlns="http://www.w3.org/2000/svg" 
     xmlns:xlink="http://www.w3.org/1999/xlink">
  <rect id="outline" stroke="black" fill="white" 
        width="100" height="100" >
    <animateTransform id="one"
                      attributeType="XML"
                      attributeName="transform"
                      type="translate"
                      from="0" to="-7"
                      dur="1s" repeatCount="1" />
    
    <!-- Doesn't work -->
    <set attributeType="XML"
         attributeName="transform"
         type="translate"
         to="-7" begin="one.end" /> 
    
    <!-- Does work (as POC) -->
    <set attributeType="css"
         attributeName="fill"
         to="green" begin="one.end" />

  </rect>
</svg>
<!-- end snippet -->

This question on persisting the end state of the animation shows how to do this with css transforms by using -webkit-animation-fill-mode: forwards;, but that obviously won't have any affect on an svg animation

fill="freeze" will persist the state of an animation e.g.

<!-- begin snippet: js hide: false --> <!-- language: lang-html -->
<svg width="200" height="200" viewBox="0 0 100 100"
     xmlns="http://www.w3.org/2000/svg" 
     xmlns:xlink="http://www.w3.org/1999/xlink">
  <rect id="outline" stroke="black" fill="white" 
        width="100" height="100" >
    <animateTransform id="one"
                      attributeType="XML"
                      attributeName="transform"
                      type="translate"
                      from="0" to="-7"
                      dur="1s" repeatCount="1"
                      fill="freeze"/>
  </rect>
</svg>
<!-- end snippet -->