purescript: change element inside SVG

Question

I have a SVG image like the following:

It is a simple SVG with a number in it. The SVG file looks something like this:

<svg ...>
  <g ...>
    <text id="my_text" ...>
      <tspan ...>
        6
      </tspan>
    </text>
    ...
  </g>
</svg>

I can load it in purescript Halogen:

import Halogen.HTML
import Halogen.Svg.Elements
import Halogen.Svg.Attributes

loadImage :: forall w i. HTML w i
loadImage = image [x 0.0, y 0.0, width 36.0, height 36.0, href "assets/my_image.svg"]

How can I programmatically change the number "6" in it? Is there something like document.getElementById("my_text") ? Can it be done with CSS?