Is there a way in XSL 1.0 to hand over variables or parameters using XSL fo:external-graphic like I would do when I'm using xsl:call-template
I know how I could work around the problem but I just wanted to know if there is a way I am not seeing.
If your SVGs are small enough, you could use fo:instream-foreign-object. (If the SVGs are very large, the size of the XSL-FO file might become a problem.)
main.xsl:
<xsl:import href="svg/svg_graphic.xsl" />
<xsl:template match="some/context">
<fo:instream-foreign-object>
<xsl:call-template name="make-svg">
<xsl:with-param name="param-a" select="..." />
</call-template>
</fo:instream-foreign-object>
</xsl:template>
svg_graphic.xsl:
<xsl:template name="make-svg">
<xsl:param name="param-a" select="..." />
<svg:svg>
...
</svg:svg>
</xsl:template>
<fo:external-graphic src="svg/svg_graphic.xsl" /> is not going to work. Inside your XSLT stylesheet, the elements in the XSL-FO namespace are just literal result elements. They are copied to the result tree, and they are not otherwise acted on by the XSLT processor. XSLT-specific attributes on literal result elements (where the attribute in the XSLT namespace and is defined as meaning something when used on literal result elements) are acted on by the XSLT processor. Attribute value templates ({...}) in attribute values of literal attributes (and some XSLT-defined attributes) are acted on by the XSLT processor.
There is no XSLT 1.0 way to get the XSLT processor to run another stylesheet based on the value of an XSL-FO-defined attribute.
There's also no XSLT 1.0 way to generate multiple result documents from one run of a stylesheet. Your XSLT processor probably has a processor-specific (or EXSLT) way to do that. The extension, if it exists, might not let you generate part of the XSL-FO result document, generate an SVG result document, and then go back to generating more of the XSL-FO document.