Hi,

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DisplayName = RF_SKILLBOOK_RAIN_FIRE

Identifiers are case sensitive; "RF_SKILLBOOK_RAIN_FIRE" is not the same as "RF_SKILLBOOK_Rain_Fire".

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e) TreasureTable.txt this is Arhu in Cyseal

You only need one 'new subtable "-1"'; the second one will clear the first table AFAIK.

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d) Unpack icons.pak, Edit Ability.dds by CS6, resave in rain_fire.dds, put in Publick/MyMod/assests/Textures/icons/

If you're only adding one ability, you shouldn't edit the existing (quite large) DDS, just create a new 64x64 DDS and put your icon in there.

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Edit in folder GUI Ability.lsx by Excel:

I'm not sure what you're editing with Excel, since the ability.lsx is an XML file, not a spreadsheet, it should definitely not be edited with Excel.

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How i can upload new dds & assign GUID?

You don't have to assign a GUID manually, just add the icon DDS to your mod (as a texture resource) using the editor, it'll generate you a new GUID automatically and create the resource .LSB file, so you don't have to do that part manually. What you have to do, is create a new .LSX in Public\YourMod\GUI, with the appropriate contents.
Sample XML:

Code
<?xml version="1.0" encoding="UTF-8" ?>
<save>
    <header version="2" time="1403875226" />
    <version major="1" minor="3" revision="0" build="0" />
    <region id="IconUVList">
        <node id="root">
            <children>
                <node id="IconUV">
                    <attribute id="MapKey" value="Portrait_Animals_Cat_Arhu" type="22" />
                    <attribute id="U1" value="0.0" type="6" />
                    <attribute id="U2" value="1.0" type="6" />
                    <attribute id="V1" value="0.0" type="6" />
                    <attribute id="V2" value="1.0" type="6" />
                </node>
            </children>
        </node>
    </region>
    <region id="TextureAtlasInfo">
        <node id="root">
            <children>
                <node id="TextureAtlasIconSize">
                    <attribute id="Height" value="64" type="6" />
                    <attribute id="Width" value="64" type="6" />
                </node>
                <node id="TextureAtlasPath">
                    <attribute id="Path" value="Public/Main/Assets/Textures/Icons/Overrides/testportraits.dds" type="29" />
                    <attribute id="UUID" value="eee08d9c-e20b-4575-b79a-87c897312601" type="22" />
                </node>
                <node id="TextureAtlasTextureSize">
                    <attribute id="Height" value="64" type="6" />
                    <attribute id="Width" value="64" type="6" />
                </node>
            </children>
        </node>
    </region>
</save>