If you mean trim the blades, you can do it, but it won't look the same. The trimmed blades will continue to grow in length, but will have squared off (and possibly browned) tips.

I've read grasses can be controlled in size by pot culture and root pruning, like Bonsai, but I haven't tried it yet. If it works, you could bury the pots in your Lily bed, and get the effect you desire.

I can't think of a Miscanthus with barred variegation which is smaller than 'Gold Bar' unless it's 'Little Zebra.' It will hit 4' to the foliage and 5' to the plumes, and from what I understand, is a faster grower than 'Gold Bar.'

I've been growing one called Miscanthus Stardust, which seems to be smaller yet than Little Zebra. Its about 3 ft of foliage at most. Narrow foliage with typical zebra-like banded gold variegation.