Hi Jason_han and welcome,
The InfoPath data is stored in XML so exporting to Excel and editing will probably not place the data in the right format for your business process. Why are you using InfoPath in the first place? To create an e-form that automates your business process, right? Excel is not an e-form editor and doesn't provide a discrete data payload for managing approvals, etc. (for example, if you have workflow requirements). Having multiple people edit the same Excel form is also a challenge to setup.
Why not just figure out why those user's can't change the form? If you are using SharePoint, maybe they just need to be granted Contribute access to the form library. If you aren't using SharePoint and the users don't have InfoPath installed, you're not going to be able to use Excel. It just won't do the same validation that the InfoPath form does.
Sorry for being the bearer or bad news, but hopefully you have SharePint and you can drink the permissions brew.
Best,
P