How to change boot picture of Windows partition?
I agree that you should test rEFInd using a flash drive. I see one can download "A USB flash drive image file" containing rEFInd. I believe you would be better off using my instructions. If you have any problems with my steps, let me know.

Steps to Install rEFInd on a USB Flash Drive


Download "A binary zip file" from The rEFInd Boot Manager:
Getting rEFInd page. I assume this will be saved in your Downloads folder.
Insert a flash drive into a USB port. Open the Disk Utility application and partition the drive as follows.



The format of the second partition does not matter. I happened to use MS-DOS (FAT). Before applying changes, click the Options... button and make sure "GUID Partition Table" is selected.



Apply the changes and quit the Disk Utility.
Open the Terminal application. Enter the following commands. You will be prompted for your log in password.

cd  downloads/refind-bin-0.8.7
./install.sh  --ownhfs  /Volumes/rEFInd  --alldrivers


This is what appeared in my Terminal window.

Last login: Fri Apr  3 01:53:35 on ttys000
Steelhead:~ davidanderson$ cd downloads/refind-bin-0.8.7
Steelhead:refind-bin-0.8.7 davidanderson$ ./install.sh --ownhfs /Volumes/rEFInd --alldrivers
Not running as root; attempting to elevate privileges via sudo....
Password:
ShimSource is none
Installing rEFInd on OS X....
Installing rEFInd to the partition mounted at /Volumes/rEFInd
Copied rEFInd binary files

Copying sample configuration file as refind.conf; edit this file to configure
rEFInd.


WARNING: If you have an Advanced Format disk, *DO NOT* attempt to check the
bless status with 'bless --info', since this is known to cause disk corruption
on some systems!!


Installation has completed successfully.

Steelhead:refind-bin-0.8.7 davidanderson$

When running rEFInd from a flash drive, I needed to introduce a 5
second delay. This delay was not needed once I installed rEFInd
on my internal hard disk. I assume you will need this temporary
delay as well. This is accomplished by editing the refind.conf
file. Enter the following commands to edit the file in the TextEdit
application. 

cd  /Volumes/rEFInd/System/Library/CoreServices
open  -e  refind.conf


At the bottom of the file, enter a line containing scan_delay 5,
as shown below.



Save the changes and quit TextEdit. If you get the following
message, just click OK.


Restart the computer. You should boot to the rEFInd boot manager. The menu that appeared on my computer is shown below. (Hint: To get a better view, open this image in a new window.)




Steps to Uninstall Automatic Booting to rEFInd


Boot to OS X.
Open "Startup Disk" from the "System Preferences" window. The "rEFInd" text, under the external disk icon, should be highlighted. 
Click on the internal disk icon representing OS X. The highlighting should switch to the text under this icon, as shown below.





Quit System Preferences, shutdown the computer and remove the USB flash drive.


What is next?

The icons files are store in the following folder.

/Volumes/rEFInd/System/Library/CoreServices/icons


It should be just a matter of substituting your icons for the default ones.

If you find any of this useful, let me know. The next step would involve installing rEFInd on your internal hard disk. I do not yet know enough about the partitioning of your internal disk to answer the questions I have. Mainly, I need to see the output from the commands given below.

diskutil list
disktuili cs list
sudo gpt -r show /dev/disk0
sudo fdisk /dev/disk0


None of these command change your computer. They only produce partitioning information.