The developers introduced this limit to ensure performance. Spore was designed in 2008, and they needed creatures to load quickly and animations to run smoothly on older hardware. But for the modern player, this limit is an anachronism.
Open the Spore Mod API Easy Installer, select your downloaded mod file, and click install. Spore Mod Unlimited Complexity
: Removes the "red bar" limit in all editors. The developers introduced this limit to ensure performance