Replace by Brush - rotorz/unity3d-tile-system GitHub Wiki
You can quickly repaint tiles which were painted using one brush with another brush. Think of this as find and replace for tiles!
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(Optional) Select tile system(s) that you would like to alter.
Skip this step if you would like to find and replace tiles for all tile systems in the scene.
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Select menu command
| Replace by Brush....The following window should then be shown:

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(Optional) Select Source Brush.
Field is automatically populated with primary brush.
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Select Replacement Brush.
All instances of source brush will be repainted with this brush.
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Specify tile system(s) which find and replace should operate on:
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Active - The active tile system.
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Selected - All editable tile systems in current selection.
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All - All editable tile systems in scene.
Caution - Always verify that this option is set correctly.
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Click Replace to perform find and replace.
Source: topics/Replace-by-Brush.md