In contrast to previous work, we demonstrate that scaffold decoration and fragment linking (or scaffold hopping) can be achieved via prompt engineering and RL with available decoder-only models. This avoids the need to design new grammars , implement and train encoder-decoder models specific to the task , or even design bespoke model architectures . In comparison to the most similar approach SAMOA, we manipulate the SMILES string and re-introduce it to the CLM iteratively such that the CLM observes all of the molecular structure at each iteration to inform conditional generation.