Canonical ACT-R supports an overwrite buffer operation that performs an end-run around the managing module and also prevents the encoding of previous contents. =goal> =chunk will replace the contents of the goal buffer with =chunk without encoding the current contents.
jACT-R does not directly support this operation. You can set, add, remove, modify or request, and that's it. You cannot circumvent the encoding. The best you can do is use the set operation which will move a chunk from one buffer to another (in 0 time). But the prior contents will still be encoded. The Lisp parser will tranform overwrites into sets automatically and notify you that this has been done.
If a retrieval fails, the only way to reset the state is to complete a successful retrieval. There is no mechanism to explicitly reset the state. While some modules do have this (+visual> isa clear), it is not standard. jACT-R solves this by using an explicit remove operation (-retrieval>). If there is nothing in the buffer, it will have its states reset.