Welcome to the Community, @barytmi.

Allow me to share information about inventory in QuickBooks Online (QBO).

In QBO, when you import 100 new products into an ongoing inventory, it will not delete your current inventory. Instead, new products will be added to the existing inventory list. 

Here's how:

1. Sign in to your QuickBooks Online account.
2. At the upper right corner of your screen, click the Gear icon ⚙.
3. Under the Tools select Import data.
4. Pick Products and Services.
5. To upload your Excel or CSV file, select Browse to upload the file from your computer. Choose the file, and then select Open.
6. Tap Next.
7. Map your information. The header of your spreadsheet represents Your Field. Select the one that corresponds to a field in your QBO from each drop-down ▼ menu.
8. Select Next.
9. If you notice red marks on the cells, this means that the cell is invalid. Try importing them again after checking the cells in your spreadsheet.
10. To replace the details of existing items in your account, select Overwrite all values for each product or service with the same name. Make sure everything is correct since we can’t undo it.
11. Once everything's settled, click Import.

Please know that once you have imported the list, it can't be undone. You can only import a thousand rows at a time. If your list is longer than that, split it into multiple and smaller files.

You can check this article for more information on importing your product and services list in your QBO account: Import products and services into QuickBooks Online.

Moreover, I’ll be adding this article for you to check out on frequently asked questions when importing data in QBO: Common questions about importing data in QuickBooks Online. 

Feel free to click "Reply" if you have more questions about importing your data into QBO. I am always here to assist you. Have a great day!