You can elect to not download quotes at the security level on the Security List (Ctrl-Y or Tools menu).
I think the issue is that you are getting the price update through your download of transactions from your brokerage/bank. When you match your Quicken security to the online (brokerage) security such that any interest payments or credits are matched, that match is going to carry on to the pricing. I think Quicken is going to 'require' some level of matching (match to an existing security or match ti a new security). Without such a match, Quicken could not process transactions for that security and your data would be mismatched between the brokerage reports and the Quicken reports. Volvogirl's suggestion to use a banking/saving cash account for the CDs is viable but may not be any smoother in the interface to the brokerage. I suggest you resign yourself to either letting Quicken use the current prices downloaded from the Brokerage/bank, or regularly deleting the prices that do get downloaded. Beyond your lack of interest in the current prices, do you see some harm in having them in the data file? The amount if data being stored for that information is minuscule in the bigger picture and not (IMO) a reason to throw it out.
If you want to keep the price fixed at $100, note that you don't have to don't have to edit the intermediate prices, just select the first price after $100, shift-click the last price to select them all, and hit Delete. Quicken will use the most recent price in the price history for market value, net worth, performance, etc.