My trust deed is very old and I would like to update it by adopting your one.
We do not "replace" trust deeds of existing trusts (except for superannuation funds) as this is highly likely to resettle the trust.
When a "resettlement" occurs, the old trust is considered to come to an end and a new one begins. This generally happens where the trustee undertakes to do something (a new "trust") not considered when the trust was first established by the original settlor - therefore, the trust has been "resettled". Effectively, the old trust disposes of all of its assets to the new trust, giving rise to CGT and stamp duty issues.
It is commonly accepted that small changes to a trust deed, such as the addition of a trust power, will not resettle the trust, but that a change to the beneficiaries, and especially the adoption of an entirely new deed, can resettle the trust.