The default behavior for matching of imported transactions and manually entered ones is to change the transaction date to the imported transaction. I would like an option to retain the manually entered date. For example: I finish my work for the year after importing my December bank statement data. I print reports and keep them in a file. Next month I download the January transactions and some of the checks I wrote in December have now changed and the new report for the previous year no longer agrees with the old one. Being able to retain the date entered would eliminate this problem.
While the default behavior has not changed, if you are using a version of KMyMoney built from master branch (developers version) you can select the matched transaction, click "unmatch", and then "match" at which point you are given the opportunity to reverse the order of the match. I'm pretty sure this will take the date from the "other" transaction. Give it a try and let us know if it works for you, or if it leads to the "wrong" choice of some other field.