Hello,
With the current structure of the upload system, there is no override capabilities and the usage of plugins (triggers) would be more appropriate.
Since you want to authorize or not the upload depending custom settings, you want to handle the files before they are handle by the upload helper (before they are moved to the right folders).
Right now the features are more around the processing of the files after they have been moved in the folder (to resize, crop, watermark, etc). The creation of settings to specify a image size is too much specific ; I would rather prefer the possibility to give several possible dimensions or a ratio, etc. Unfortunately I do not see any ideal implementation right now so the usage of a plugin would be best to unsure the flexibility.
It might be something we can add before the next release (HikaMarket 3) but I would need the maximum details about your specifications.
Regards,