As you've figured out the best way to deal with assets is to have LS scan it first then edit in the information afterwards. This is by design.
An alternative method for tracking assets is to use the Asset Relations to tie the manually created asset to the LS scanned asset.
Create a Relation Type called "Same As" in Configuration, Relational Mapping.
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Next in your newly scanned LS asset, edit asset and under Asset Relations, add This Asset (LS scanned), Type (Same As), Select Asset (Manually created asset), add notes as desired, Add.
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Save asset and now the two are linked.
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Now whenever you need to access the starting point of the asset's life, you have a paper trail as it were.
Good luck.