Yes, but you would have to edit each transaction 1 by 1.
You can turn the option of classes off, also.

Resolution for 'classes assigned issue: 'Is it possible to remove the classes assigned years ago (which I no longer use) to clean up my Premier 2017 desktop books and report properly?' available: Yes.

The classes assigned issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the classes assigned issue yourself by looking for a resolution described in the article. If it is a complex classes assigned issue or you are unable to solve the issue, you may contact us by clicking here or by using other classes assigned support options.

For more information about resolving issues related to classes assigned in Quickbooks/QBO or to get support for the issue 'Is it possible to remove the classes assigned years ago (which I no longer use) to clean up my Premier 2017 desktop books and report properly?', click the link below: