[Suggestion] [Editor] Bring back the replace feature

[Strato Incendus]

I think I've found a way to solve two remaining issues with the new editor and level conversion at one fell swoop!

One of the few remaining distinctive features of the old formats editor - and one of the main reasons why people like Arty and me oftentimes still prefer the old editor - is the option to replace a piece that has already been placed in the level by hitting F9 and selecting a different piece from the list. This allows for several things:

1) Quickly selecting a new piece from the same tileset as the selected piece while the main graphic set may be a different one (for example, your main tileset is pillar, but you've taken a trap from dirt, and want to exchange it for another trap from dirt)
2) Replacing a piece with a tile from a different graphic set while keeping it in the exact same spot

It is the latter that would simultaneously also solve the issue we currently still have going on with the Ancient tileset (and also my custom edits to the old original Lemmings graphic sets, btw!) .

If a replace feature, as it has already been present in the old editor, also existed in new formats, one could do the following:

1) Create a temporary conversion of the complete old Ancient tileset.
2) Load up the level in the new editor.
3) Select the pieces from the ancient tileset and replace them with the identical pieces from "angel island" or "chaos angel", in this case. Everything now remains in the exact same spot as before!
4) Once all tiles have been replaced with their counterparts, delete the temporary conversion of the Ancient tileset. The level from now on consists of tiles from "angel island" and "chaos angel".

I could do the same with my custom edits of the fire, brick, and pillar tileset, of course: Temporarily convert mine, replace all tiles with the identical ones from the standard new formats versions, then delete my custom conversion.

I wouldn't be requesting this if it were only to fix my own mess with regards to the custom edits of the standard lemmings graphic sets . As I said, it also solves the issue with the Ancient tileset that has been split up into two sets in new formats, and that affects anyone who has ever used Ancient.

And, most of all, this tile replacement option is simply a generally useful and convenient feature that has been present in the old formats version anyway, and many users have come to enjoy it!

[Crane]

I like to agree with this one.  I myself used it when converting Colorful Arty's "Hailfire Peaks" for Holiday Lemmings '16.  When it was originally designed, he used a custom tileset that merged everything together, but by the time Holiday Lemmings '16 was out, the ability to use multiple tilesets in a single level had been introduced, so I painstakingly replaced every single tile to the regular Snow and Fire ones, with the intention of bringing down the file size of the final pack (i.e. not having to distribute the massive merged tileset with the pack).

Additionally, it would prove very useful if one were trying to re-create an old level in a new tileset.  For example, I've been re-creating a number of Fun levels in different tilesets for my "Challenge" rating, which returns players to levels from the original games with a severely reduced skillset with which to complete the level with.