SlickFloss is right, it is specifically prohibited, if you read the regs. Reading the rules, explains the rules.
See definition of distillation: https://www.ecfr.gov/current/title-27/chapter-I/subchapter-A/part-19/subpart-L/subject-group-ECFR3229fff77eb967f/section-19.301
"However, the quantity and proof of any unfinished spirits must be determined and recorded before any mingling with other materials or before any further operations involving the unfinished spirits outside the continuous system". Since you are breaking the continuous system, i.e. changing mash bills and starting another production run you need to identify the unfinished spirit and place it into storage.
See identification of spirits: https://www.ecfr.gov/current/title-27/chapter-I/subchapter-A/part-19/subpart-L/subject-group-ECFR3229fff77eb967f/section-19.305
"When the proprietor intends to enter spirits into storage on bonded premises for later packaging in wooden packages, the proprietor may identify the spirits with the designation to which they would be entitled if drawn into wooden packages, followed by the word “Designate,” for example, “Bourbon Whisky Designate.”"
See definitions of whiskeys: https://www.ecfr.gov/current/title-27/chapter-I/subchapter-A/part-5/subpart-I/section-5.143
"Fermented mash of not less than 51%, respectively: Corn" means just that, not a blend of distillates that result in that.