Is there any way to append the current date to a defined (not the default of the IMAGEID) backup file name when it is created?

No.  This feature has been requested many times but has not made it into the product - yet.

Don't forget though that it is very easy to see the dates and times created for each backup file in the list under the Image Restore tab within Reflect.  It is also easy see the date created for each file from within File Explorer.

(Sorry for my English)

Sorry but no, it isn't; or better, it's easy to see when Windows created the file, not when Macrium created the backup file. Problems happen when moving or duplicating backups to another HD.
In File Explorer it is possibile display "Backup Method" and "Backup Comment", but "Backup Time" is available only in file properties.

It would be great to have a "Backup date" column in File Explorer (maybe in ISO format)
Cheers.  G