An interesting idea, but how would we handle LTEX records shared between LAND records. Perhaps I'm misunderstanding the structure, but don't all LAND records in a plugin access a shared pool of LTEX records? Assuming my understanding is right, this brings up another potential issue. If the user changes an LTEX record, they could be trying to do it only for a single cell, or for a large grouping of cells (maybe even all of them).
Maybe it's just me, but since LTEX records are plugin specific anyway, it doesn't seem worthwhile or intuitive to mark them as modified. I think LTEX records should be thought of more as a palette. If they exist in other plugins, when the user uses them, they are brought into the current plugin palette. The user can choose to add or remove LTEX records from their palette manually. They can also choose to change what texture the LTEX record in their palette points to. If a LTEX record is removed, any modified LAND records that reference it will have those "references" be set to 0 (which specifies that the default texture will be used). When a LAND record is modified, any LTEX records it references that don't exist in the current palette are added automatically. We could then provide extended tools for changing an LTEX record across multiple LAND records.