Some ideas if you want your custom pattern only for some special display
purposes:
Create a textbox with dimensions of a cell, properties - Move & size with
cell.
Format fill - effect - picture (your pattern image file)
Put the cursor in the textbox
In the Input bar type an = followed by some cell reference.
or
Create textboxes to exactly fit cells and = cell ref as above.
Format each with thin grey broder
Format fill color with no fill / invisible
Add a picture to the sheet with your image, over the textboxes.
Order - send to back
or similarly format a recangle with fill effect - picture -your image
or
Format - sheet - background
applies to entire sheet and will not print
Regards,
Peter T