Probably the best idea would be to set up a completely empty document
end define all the necessary styles, that you like to have for the
lists, for the paragraph spacing, etc.
Then copy the original document, but while copying, make sure that the
document updates all style settings to correspond to the new defined
settings of the empty document. Especially, that can be tricky though,
if you have numbered formulas in your documents, and you have to
combine several documents.