Recompile firmware to add new kernel modules best practicle

I have seen sometimes I need new firmware to add new kernel modules to support i2C, usb camera etc (kmod-xxx).
Therefore I need new build/firmware. I have seen If I make new module as xxx.ipk it is not more compatible with the old kernel.
The 3.18.29-abcd, abcd will be different.

Is it some best practicle how can I reserve the old installations when I update the kernel?
Is it possible to avoid everytime to reinstall packages and configurations?
Buildroot or imagebuilder can help? I do not want to set in config all modules to <m>.