I have not done it yet myself but I have seen several posts pointing to an easy solution in the image builder config file(s). Here is a link to one such forum topic: Image builder filesize "out of space"
I and others have posted info on expanding the writable filesystems after installation on SD cards for the R4S and devices with similar storage layout. They may not apply if there are additional filesystems for wifi data or another storage layout etc.
Here is a link to instruction for f2fs filesystem type: https://github.com/anaelorlinski/OpenWrt-NanoPi-R2S-R4S-Builds/blob/main/docs/resize-f2fs.md
Here is a link to my forum topic if the writable filesystem is ext4: Resizing the hidden overlay filesystem when it is ext4 and not f2fs
Keep in mind that typically for devices with the simple filesystem layout I'm familiar with, the installer and upgrade process both overwrite the partition table and file systems so the extra space and all data get wiped out every time. You need to backup any data you want to restore after each upgrade being mindful not to overwrite upgraded files.
It may be useful to always add new packages by building a new custom image with the additional items and disk sizes, install it and restore your configs etc.