Historical Rules · 26 September 2015
Rule 702.46b
Official source text from the 26 September 2015 Rules release
You can’t choose to use a splice ability if you can’t make the required choices (targets, etc.) for that card’s instructions. You can’t splice any one card onto the same spell more than once. If you’re splicing more than one card onto a spell, reveal them all at once and choose the order in which their instructions will be followed. The instructions on the main spell have to be followed first.