what version of messenger is this? You might want to take a look at how I replaced the Shopping trolly icon in mobile chat windows in Vistafy, if you download and install it open 920 Definition and Style .txt's and search (Ctrl+F) buycreditsbtn and see in the style file the ButtonIcon part for it, I had to rename the icon resource, you'll see what it was renamed too out of frustration mostly
(some dodgyness of WLM) and reference it in the definition.
This way you can circumvent the RLE restrictions in 9.0 and 8.5 if necessary
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