Marketo's learning passport has a landing pages course next week that still has some availability. This is an interactive class, so if you don't get your question answered, perhaps it could be answered then. Here's the courses page: https://student.gototraining.com/6f598/catalog/1766512024711156480
Here is a tutorial on making emails editable, perhaps this could work for landing pages too? https://community.marketo.com/MarketoTutorial?id=kA250000000Kz3bCAC
Or perhaps you could achieve your goal with dynamic snippets? https://community.marketo.com/MarketoDeepDive?id=kA5500000008T2TCAU#powerful