Hi Verrex,
Thanks for using Syncfusion products.
1. You cannot import the text that start with "=". But you can import it by giving double quote to that text. Example "=Hai".
2. You cannot set the format of the cell befor you import.
Please refer to the sample in the below link which illustrates the above.
http://websamples.syncfusion.com/samples/XlsIO.Web/6.1.0.34/F70649/main.htmPlease let us know if you have any other concerns. We will be glad to assist you.
Regards,
Vinoth