If I may:
I used to answer questions about the suitability of certain tires on particular vehicles. It is a question chock full of pitfalls as answering in the affirmative gives a sharp lawyer a point of leverage.
So you will rarely find a tire manufacturer directly answering these kinds of questions. They will always be cloaked in qualifiers or vague terms, if they are answered at all.
In the case of ST tires, since there is virtually no commonality in tire size, it is easy for a tire manufacturer to avoid the pitfalls by stating that an LT tires is not a suitable replacement for an ST tire - and that would be correct since there is no tire size that directly corresponds.
But if certain factors are accounted for, then an LT tire COULD be used as a replacement - BUT - a tire manufacturer will want to shift the legal burden to the person making that decision and not take it on themselves.
I hope everyone is clear on this point as it can be a source of difference as to what a person does. What one person feels is the right move can be different than someone else's. If you can't understand and respect why someone would do something different than what you would do, then perhaps you shouldn't be posting.