Yes, but make sure you check with your host to verify that the extension change is necessary.

Apache servers (which is what most hosts use) can be configured to serve SSI files without the ".shtml" extension. If your host's server is configured for the feature, the server will treat any ".html" file as an SSI file if its user execute bit is set [chmod u+x file.html]. (All of the files on my site are SSI [for now], but they use the standard ".html" extensions.)

You could find out if it works on your server by setting the execute bit on a test file that has a standard ".html" extension and that has <!--#include ... commands. Try to open it to see if the server parses the file for the includes.

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