The antonym of "attached weight to" would be "lifted weight from" or "removed weight from." This means that instead of adding weight to an object, you are taking weight away from it. It could also mean that you are making something lighter or relieving its burden, rather than making it heavier. This may be useful in situations where you need to reduce the load on a particular object, such as when unloading cargo from a truck or ship. The opposite of attaching weight to something can also apply to psychological or emotional burdens, where removing something can lead to a feeling of lightness or release.