Can I use peach jam in gingerbread sandwich cookies?

This is really personal taste preference.

While I have not tried either recipe, having multiple decades of experience eating gingerbread and various jams, I would think peach jam would work fine.

I have never had coconut Linzer cookies, but I’ve had plenty of coconut in my day. This might work okay even if peaches and coconuts don’t grow in the same region.

The sensible approach would be to make each recipe as directed and use peach jam in one cookie as a comparison.

Some people might enjoy it, undoubtedly some people won’t be quite as keen. In the end, you will be serving them to *YOUR* guests so do what you think will please them.

Best of luck.

It'd taste fine, but you couldn't call them Linzer cookies- or shouldn't anyway.