Install the plugin by downloading the gplugin file and dragging it in to Geneious or use the plugin manager in Geneious (under Tools - Plugins in the menu).
Once installed, run the plugin by selecting a sequence and selecting either Generate Mutated Sequences or Generate Shuffled Sequences from the Sequence menu.
EMBOSS: The European Molecular Biology Open Software Suite (2000)
Rice,P. Longden,I. and Bleasby,A.
Trends in Genetics 16, (6) pp276--277