What if we allowed

ext.prefix2

as well as

ext.prefix

? That'd make the proposed change to the bwa/index modules to be changed, e.g. https://github.com/nf-core/modules/pull/9997 as well as fixing bamcmp (https://github.com/nf-core/modules/blob/master/modules/nf-core/bamcmp/main.nf). @Jim Downie, I see you actually suggested it on that linked PR above. It'd be consistent with the way we allow

ext.args, ext.args2

. 👍 /👎 /🤷 anyone?