[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] MattBooth:
I think I changed those because it didn't work the first time... but I honestly can't recall. Let me try what you're suggesting :)

EDIT:

Same error if I follow the OP to the letter.

If you notice:

[COLOR="RoyalBlue"]const-string v17, "lockscreen_sounds_enabled"

const/16 v19, 0x1

move-object/from16 v0, v17

move/from16 v1, v19

invoke-static {v14, v0, v1}, Landroid/provider/Settings$System;->getInt(Landroid/content/ContentResolver;Ljava/lang/String;I)I

move-result v17

if-eqz v17, :cond_f

const/16 v17, 0x1

:goto_6
move-object/from16 v0, v18

move/from16 v1, v17

invoke-virtual {v0, v1}, Landroid/preference/CheckBoxPreference;->setChecked(Z)V[/COLOR]

[COLOR="Red"]const-string v18, "volbtn_music_controls"

move-object/from16 v0, p0

move-object/from16 v1, v18

invoke-virtual {v0, v1}, Lcom/android/settings/SoundSettings;->findPreference(Ljava/lang/CharSequence;)Landroid/preference/Preference;

move-result-object v18

check-cast v18, Landroid/preference/CheckBoxPreference;

move-object/from16 v0, v18

move-object/from16 v1, p0

iput-object v0, v1, Lcom/android/settings/SoundSettings;->mVolBtnMusicCtrl:Landroid/preference/CheckBoxPreference;

move-object/from16 v0, p0

iget-object v0, v0, Lcom/android/settings/SoundSettings;->mVolBtnMusicCtrl:Landroid/preference/CheckBoxPreference;

move-object/from16 v18, v0

const/16 v19, 0x0

invoke-virtual/range {v18 .. v19}, Landroid/preference/CheckBoxPreference;->setPersistent(Z)V

move-object/from16 v0, p0

iget-object v0, v0, Lcom/android/settings/SoundSettings;->mVolBtnMusicCtrl:Landroid/preference/CheckBoxPreference;

move-object/from16 v19, v0

const-string v18, "volbtn_music_controls"

const/16 v20, 0x1

move-object/from16 v0, v18

move/from16 v1, v20

invoke-static {v15, v0, v1}, Landroid/provider/Settings$System;->getInt(Landroid/content/ContentResolver;Ljava/lang/String;I)I

move-result v18

if-eqz v18, :cond_long

const/16 v18, 0x1

:goto_long
move-object/from16 v0, v19

move/from16 v1, v18

invoke-virtual {v0, v1}, Landroid/preference/CheckBoxPreference;->setChecked(Z)V[/COLOR]

Look at the blue compared to the red. The blue is straight from my smali file, the red is from the guide. The vXX numbers are totally different, where as in the OP:

[COLOR="red"]const-string v18, "lockscreen_sounds_enabled"

const/16 v20, 0x1

move-object/from16 v0, v18

move/from16 v1, v20

invoke-static {v15, v0, v1}, Landroid/provider/Settings$System;->getInt(Landroid/content/ContentResolver;Ljava/lang/String;I)I

move-result v18

if-eqz v18, :cond_f

const/16 v18, 0x1

:goto_6
move-object/from16 v0, v19

move/from16 v1, v18

invoke-virtual {v0, v1}, Landroid/preference/CheckBoxPreference;->setChecked(Z)V[/COLOR]

.line 291
const-string v18, "volbtn_music_controls"

move-object/from16 v0, p0

move-object/from16 v1, v18

invoke-virtual {v0, v1}, Lcom/android/settings/SoundSettings;->findPreference(Ljava/lang/CharSequence;)Landroid/preference/Preference;

move-result-object v18

check-cast v18, Landroid/preference/CheckBoxPreference;

move-object/from16 v0, v18

move-object/from16 v1, p0

iput-object v0, v1, Lcom/android/settings/SoundSettings;->mVolBtnMusicCtrl:Landroid/preference/CheckBoxPreference;

move-object/from16 v0, p0

iget-object v0, v0, Lcom/android/settings/SoundSettings;->mVolBtnMusicCtrl:Landroid/preference/CheckBoxPreference;

move-object/from16 v18, v0

const/16 v19, 0x0

invoke-virtual/range {v18 .. v19}, Landroid/preference/CheckBoxPreference;->setPersistent(Z)V

move-object/from16 v0, p0

iget-object v0, v0, Lcom/android/settings/SoundSettings;->mVolBtnMusicCtrl:Landroid/preference/CheckBoxPreference;

move-object/from16 v19, v0

const-string v18, "volbtn_music_controls"

const/16 v20, 0x1

move-object/from16 v0, v18

move/from16 v1, v20

invoke-static {v15, v0, v1}, Landroid/provider/Settings$System;->getInt(Landroid/content/ContentResolver;Ljava/lang/String;I)I

move-result v18

if-eqz v18, :cond_long

const/16 v18, 0x1

:goto_long
move-object/from16 v0, v19

move/from16 v1, v18

invoke-virtual {v0, v1}, Landroid/preference/CheckBoxPreference;->setChecked(Z)V

They match.

SAme for this part of my smali file:

goto/16 :goto_5

:cond_f
const/16 v17, 0x0

goto/16 :goto_6

:cond_long
const/16 v18, 0x0

goto/16 :goto_long

Clearly that needs to be v17 not v18, as in the OP, they're all v18, so I assume it needs to be adjusted to match my smali.

The issue here is that they need to match, and I don't understand the smali assembly language enough to match them myself.