Do I understand your question correctly? You have a Word document that contains, I'm assuming, the texty part of a contract or business proposal and you've linked it to Excel, which does the numbers part.
I've encountered the SQL dialog box myself and discovered that if it's the same Word doc and same Excel file (no name changes or saving to a different folder), it doesn't come up. But that's not very real world, is it? You want to be able to save a unique Excel spreadsheet for each client/customer.
Would embedding the Excel spreadsheet work for you? Or is it multiple worksheets long?
In your Word document TEMPLATE, go to Insert Ribbon > Text Section (near right end) > Objects. Choose Create New tab and choose Microsoft Excel Worksheet. If it is really large or multiple worksheets, click the Display as Icon checkbox. Otherwise, you can make it look like a table in your Word document, but have all the Excel tools.
Be sure to save your Word template as a template, then double-click on it in File Explorer to create a new contract for every customer. Bonus feature: you'll never have to worry about accidentally overwriting an existing contract.